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ICQ
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ICQ
Original authorMirabilis
Developers
Initial releaseNovember 15, 1996; 29 years ago (1996-11-15)
Final release
10.0.46867 (May 27, 2022)
Repository
Written in
Platform
Available in
  • Russian
  • English
  • Hebrew
  • Portuguese
  • Ukrainian
  • German
  • Czech
  • French
  • Chinese
  • Turkish
  • Spanish
  • Arabic
  • Vietnamese
TypeInstant messaging
LicenseProprietary
Websiteicq.com

ICQ was a cross-platform instant messaging (IM) and VoIP client founded in June 1996 by Yair Goldfinger, Sefi Vigiser, Amnon Amir, Arik Vardi, and Arik's father, Yossi Vardi. The name ICQ derives from the English phrase "I Seek You".[1] Originally developed by the Israeli company Mirabilis in 1996, the client was bought by AOL in 1998, and then by Mail.Ru Group (now VK) in 2010.[2]

The ICQ client application and service were initially released in November 1996, freely available to download. The business did not have traditional marketing and relied mostly on word-of-mouth advertising instead, with customers telling their friends about it, who then informed their friends, and so on.[3] ICQ was among the first stand-alone instant messenger (IM) applications—while real-time chat was not in itself new (Internet Relay Chat [IRC] being the most common platform at the time), the concept of a fully centralized service with individual user accounts focused on one-on-one conversations set the blueprint for later instant messaging services like AIM,[4] and its influence is seen in modern social media applications. ICQ became the first widely adopted IM platform.[5]

At its peak around 2001, ICQ had more than 100 million accounts registered.[1] At the time of the Mail.Ru acquisition in 2010, there were around 42 million daily users.[6] In 2022, ICQ had about 11 million monthly users.[7]

The service was shut down on June 26, 2024, following an announcement on ICQ's website in May 2024.[8]

Features of ICQ New

[edit]

The last version of the service, launched in 2020 as "ICQ New", featured a number of different messaging functions:

  • Private chats: conversations between two users, with history synchronized to the cloud. A user could delete a sent message at any time, and a notification will be shown indicating that the message has been deleted.
  • A chat with oneself, which could be used to save messages from group or private chats, or upload media content as a form of cloud storage.
  • Group chats with up to 25,000 participants at the same time, which any user could create. Users could hide their phone number from other participants, see which group members have read a message, and switched off notifications for messages from specific group members.
  • Audio and video calls with up to five people.
  • Sending and receiving of audio messages, with automatic transcription to text.
  • Channels, where authors could publish posts as text messages and attach media files, similar to a blog. Once the post was published, subscribers receive a notification as they would from regular and group chats. The channel author could remain anonymous.
  • Polls inside group chats.
  • An API-bot which could be used by anyone to create a bot, to perform specific actions and interact with users.
  • "Stickers": small images or photos expressing some form of emotion that could be selected from a provided sticker library or users could upload their own. Machine learning was used to recommend stickers automatically.
  • "Masks": images that could be superimposed onto the camera in real-time during video calls, or onto photos to be sent to other users.
  • Nicknames, which users could set to use in place of a phone number for others to search for and contact them.
  • "Smart answers": short phrases that appear above the message box which can be used to answer messages. ICQ New analyzed the contents of a conversation and suggests a few pre-set answers.

UIN

[edit]

ICQ users were identified and distinguished from one another by UIN, or User Identification Numbers, distributed in sequential order. The UIN was invented by Mirabilis, as the user name assigned to each user upon registration. Issued UINs started at '100,000' (six digits) and every user received a UIN when first registering with ICQ. As of ICQ6 users were also able to log in using the specific e-mail address they associated with their UIN during the initial registration process. Unlike other instant messaging software or web applications, on ICQ the only permanent user info was the UIN, although it was possible to search for other users using their associated e-mail address or any other detail they made public by updating it in their account's public profile. In addition the user could change all of his or her personal information, including screen name and e-mail address, without having to re-register. Since 2000, ICQ and AIM users were able to add each other to their contact list without the need for any external clients. As a response to UIN theft or sale of attractive UINs, ICQ started to store email addresses previously associated with a UIN.[9] As such UINs that are stolen could sometimes be reclaimed, if a valid primary email address was entered into the user profile.

History

[edit]

The founding company of ICQ, Mirabilis, was established in June 1996 by five Israeli developers: Yair Goldfinger, Sefi Vigiser, Amnon Amir, Arik Vardi, and Arik's father Yossi Vardi.[10] ICQ was one of the first text-based messengers to reach a wide range of users.[11]

The technology Mirabilis developed for ICQ was distributed free of charge. The technology's success encouraged AOL to acquire Mirabilis on June 8, 1998, for $287 million up front and $120 million in additional payments over three years based on performance levels.[12] In 2002 AOL successfully patented the technology.[13][14]

After the purchase, the product was initially managed by Ariel Yarnitsky and Avi Shechter. ICQ's management changed at the end of 2003. Under the leadership of the new CEO, Orey Gilliam,[15] who also assumed the responsibility for all of AOL's messaging business in 2007, ICQ resumed its growth; it was not only a highly profitable company, but one of AOL's most successful businesses. Eliav Moshe replaced Gilliam in 2009 and became ICQ's managing director.[16]

ICQ logo, used from 2015 to 2020

In April 2010, AOL sold ICQ to Digital Sky Technologies, headed by Alisher Usmanov, for $187.5 million.[17] While ICQ was displaced by AOL Instant Messenger, Google Talk, and other competitors in the US and many other countries over the 2000s, it remained the most popular instant messaging network in Russian-speaking countries, and an important part of online culture.[18] Popular UINs demanded over 11,000₽ in 2010.[18]

In September of that year, Digital Sky Technologies changed its name to Mail.Ru Group. Since the acquisition, Mail.ru has invested in turning ICQ from a desktop client to a mobile messaging system. As of 2013, around half of ICQ's users were using its mobile apps, and in 2014, the number of users began growing for the first time since the purchase.[6]

In March 2016, the source code of the client was released under the Apache license on GitHub.[19][20]

ICQ logo, debuted in 2020

In 2020, Mail.Ru Group decided to launch a new version, "ICQ New", based on the original ICQ. The updated software was presented to the general public on April 6, 2020.[21]

During the second week of January 2021, ICQ saw a renewed increase in popularity in Hong Kong, spurred on by the controversy over WhatsApp's privacy policy update. The number of downloads for the application increased 35-fold in the region.[22]

On May 24, 2024, the main page of ICQ's website announced that the service would be shutting down on June 26, 2024.[8] ICQ recommended that users migrate to VK Messenger and VK WorkSpace.[23]

Development history

[edit]
  • ICQ 99a/b the first releases that were widely available.
  • ICQ 2000 incorporated into Notes and Reminder features.
  • ICQ 2001 included server-side storage of the contact list. This provided synchronization between multiple computers and enforced obtaining consent before adding UINs to the contact list by preventing clients from modifying the local contact list directly.
  • In 2002, AOL Time Warner announced that ICQ had been issued a United States patent for instant messaging.
  • ICQ 2002 was the last completely advertising-free ICQ version.
  • ICQ Pro 2003b was the first ICQ version to use the ICQ protocol version 10. However, ICQ 5 and 5.1 use version 9 of the protocol. ICQ 2002 and 2003a used version 8 of the ICQ protocol. Earlier versions (ICQ 2001b and all ICQ clients before it) used ICQ protocol version 7.
  • ICQ 4 and later ICQ 5 (released on Monday, February 7, 2005), were upgrades on ICQ Lite. One addition was Xtraz, which offers games and features intended to appeal to younger users of the Internet. ICQ Lite was originally an idea to offer the lighter users of instant messaging an alternative client which was a smaller download and less resource-hungry for relatively slow computers.
  • ICQ 5 introduced skins support. There are few official skins available for the current ICQ 5.1 at the official website; however, a number of user-generated skins have been made available for download.
  • ICQ 6, released on April 17, 2007, was the first major update since ICQ 4. The user interface has been redesigned using Boxely, the same rendering engine used in AIM Triton. This change adds new features such as the ability to send IMs directly from the client's contact list. ICQ has recently started forcing users of v5.1 to upgrade to version 6 (and XP). Those who do not upgrade will find their older version of ICQ does not start up. Although the upgrade to version 6 should be seen as a positive thing, some users may find that useful features such as sending multiple files at one time is no longer supported in the new version. At the beginning of July 2008, a network upgrade forced users to stop using ICQ 5.1 – applications that identified themselves as ICQ 5, such as Pidgin, were forced to identify themselves as ICQ 6. There seems to be no alternative for users other than using a different IM program or patching ICQ 5.1 with a special application.
  • ICQ 7.0, released on January 18, 2010. This update includes integration with Facebook and other websites. It also allows custom personal status similar to Windows Live Messenger (MSN Messenger). ICQ 7.0 does not support traditional Chinese on standard installation or with the addition of an official language pack. This has made its adoption difficult with the established user base from Hong Kong and Taiwan where traditional Chinese is the official language.
  • ICQ 8, released on February 5, 2012 – "Meet the new generation of ICQ, Enjoy free video calls, messages and SMS, social networks support and more."
  • ICQ 10.0, released January 18, 2016. Final update was 10.0 Build 46867, released on May 27, 2022.[24]

Criticism

[edit]

Policy against unofficial clients

[edit]

AOL (and later Mail.ru) pursued an aggressive policy regarding alternative ("unauthorized") ICQ clients.

  • In July 2008, changes were implemented on ICQ servers causing many unofficial clients to stop working. These users received an official notification from "ICQ System".
  • On December 9, 2008, another change to the ICQ servers occurred: clients sending Client IDs not matching ICQ 5.1 or higher stopped working.
  • On December 29, 2008, the ICQ press service distributed a statement characterizing alternative clients as dangerous.[25]
  • On January 21, 2009, ICQ servers started blocking all unofficial clients in Russia and Commonwealth of Independent States countries.[26] Users in Russia and Ukraine received a message from UIN 1:

"Системное сообщение

ICQ не поддерживает используемую вами версию. Скачайте бесплатную авторизованную версию ICQ с официального web-сайта ICQ.

System Message

The version you are using is not supported by ICQ. Download a free authorized ICQ version from ICQ's official website."

On icq.com there was an "important message" for Russian-speaking ICQ users: "ICQ осуществляет поддержку только авторизированных версий программ: ICQ Lite и ICQ 6.5." ("ICQ supports only authorized versions of programs: ICQ Lite and ICQ 6.5.")

  • On February 3, 2009, the events of January 21 were repeated.
  • On December 27, 2018, ICQ announced it was to stop supporting unofficial clients, affecting many users who prefer a compact size using Miranda NG and other clients.
  • On December 28, 2018, ICQ stopped working on some unofficial clients.
  • In late March, 2019, ICQ stopped working on the Pidgin client, as initiated in December 2018.

Cooperation with Russian intelligence services

[edit]

According to a Novaya Gazeta article published in May 2018, Russian intelligence agencies had access to online reading of ICQ users' correspondence during crime investigations. The article examined 34 sentences of Russian courts, during the investigation of which the evidence of the defendants' guilt was obtained by reading correspondence on a PC or mobile devices. In six of the fourteen cases in which ICQ was involved, the capturing of information occurred before the seizure of the device. Because the rival service Telegram blocks all access for the agencies, the Advisor of the Russian President, German Klimenko, recommended to use ICQ instead.[27]

Child pornography

[edit]

In 2023, an investigation by Brazilian news outlet Núcleo Jornalismo found that ICQ was used to freely share child pornography due to lax moderation policies.[28]

Clients

[edit]

AOL's OSCAR network protocol used by ICQ was proprietary and using a third party client was a violation of ICQ Terms of Service. Nevertheless, a number of third-party clients were created by using reverse-engineering and protocol descriptions. These clients included:

  • Adium: supports ICQ, Yahoo!, AIM, MSN, Google Talk, XMPP, and others, for macOS
  • Ayttm: supports ICQ, Yahoo!, AIM, MSN, IRC, and XMPP
  • BitlBee: IRC gateway, supports ICQ, Yahoo!, AIM, MSN, Google Talk, and XMPP
  • Centericq: supports ICQ, Yahoo!, AIM, MSN, IRC and XMPP, text-based
  • climm (formerly mICQ): text-based
  • Jimm: supports ICQ, for Java ME mobile devices
  • Kopete: supports AIM, ICQ, MSN, Yahoo, XMPP, Google Talk, IRC, Gadu-Gadu, Novell GroupWise Messenger and others, for Unix-like
  • Meetro: IM and social networking combined with location; supports AIM, ICQ, MSN, Yahoo!
  • Miranda NG: supports ICQ, Yahoo!, AIM, MSN, IRC, Google Talk, XMPP, Gadu-Gadu, BNet and others, for Windows
  • Naim: ncurses-based
  • Pidgin (formerly Gaim): supports ICQ, Yahoo!, AIM, Gtalk, MSN, IRC, XMPP, Gadu-Gadu, SILC, Meanwhile, (IBM Lotus Sametime) and others
  • QIP: supports ICQ, AIM, XMPP and XIMSS
  • stICQ: supports ICQ, for Symbian OS
  • Trillian: supports ICQ, IRC, Google Talk, XMPP and others

AOL supported clients include:

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

ICQ

View on Grokipedia
from Grokipedia
ICQ (pronounced "I seek you") was a cross-platform client developed by the Israeli company Mirabilis and first released in November 1996. Upon registration, users received a unique numerical identifier known as a UIN (User Identification Number), which served as a persistent for locating and messaging contacts regardless of screen names or addresses. The service pioneered real-time text-based communication over the , including features such as multi-user chat rooms, offline message queuing, and resumable file transfers, amassing tens of millions of users by the late 1990s. Mirabilis, the original developer, was acquired by America Online () in June 1998 for $287 million, after which ICQ integrated with AOL's ecosystem but retained its distinct identity. Ownership later transferred to Mail.ru Group (now VK) in 2010, and the service operated until its discontinuation on June 26, 2024, marking the end of one of the earliest widespread platforms.

History

Early Development and Launch (1996–1998)

ICQ was developed by Mirabilis, an Israeli startup founded in July 1996 by four young programmers—Arik Vardi, Yair Goldfinger, Sefi Vigiser, and Amnon Amir—who had connected through shared computing interests and prior collaborations. The team, mostly in their early twenties and lacking significant funding, completed the core software in under two months using a architecture with a central server for user presence detection. The initial version of ICQ, an acronym for "I Seek You," launched on November 15, 1996, as a free Windows client enabling real-time between users identified by unique numerical IDs (UINs). Key features included automatic notifications of friends' online status, a searchable global directory for discovering users, multi-user chat rooms, asynchronous offline delivery, and resumable file transfers—capabilities that distinguished it from earlier IRC-based systems by prioritizing simplicity and personal connectivity over channel-based discussions. Without traditional marketing, adoption spread virally among early users, reaching nearly half a million registrations within months. By 1997, ICQ's user base had surged into the millions, fueled by its accessibility on dial-up connections and appeal to global audiences, with over 10 million users reported as the service gained traction outside the U.S. Growth accelerated in 1998, adding approximately one million users every three weeks and approaching 12 million registered accounts by mid-year, with about 60% of users international and nearly 40% in Europe. This rapid expansion, driven by word-of-mouth and the novelty of instant personal notifications, positioned ICQ as the dominant instant messaging platform before its acquisition by AOL in June 1998 for $287 million.

Acquisition by AOL and Expansion (1998–2005)

In June 1998, acquired Mirabilis, the Israeli developer of ICQ, for $287 million in cash. The deal, announced on June 8 and completed shortly thereafter, was driven by ICQ's established user base of nearly 12 million registered users at the time, which complemented AOL's domestic dominance with AOL Instant Messenger (AIM) while providing a foothold in international markets where ICQ had gained traction outside the . Under AOL's ownership, ICQ's registered user base expanded rapidly, growing tenfold to over 100 million by the early , fueled by viral adoption in , Asia, and other non-U.S. regions where AOL leveraged local partnerships for distribution. This growth reflected ICQ's appeal as a free, cross-platform messaging tool, though remained challenging despite efforts to integrate and premium features. AOL enhanced ICQ's functionality to position it as a "desktop communication portal," adding elements like web search integration, pages, and desktop news feeds by 1999 to encourage prolonged user sessions. The release of ICQ 2000a in May 2000 introduced a redesigned , quick-launch , improved preferences interface, firewall compatibility, and multi-language support, alongside features such as notes, reminders, and enhanced encryption in subsequent updates like ICQ 2000b. Interoperability efforts bridged ICQ with AOL's ecosystem; starting with beta tests in fall 2000 that allowed AIM users to view ICQ contacts, full cross-network messaging between AIM and ICQ users was enabled by June 2003, creating a combined network potentially reaching 138 million users and expanding ICQ's reach within AOL's .

Transition to Mail.ru Ownership and Stagnation (2005–2024)

In 2010, (AOL) sold ICQ to Mail.ru Group, a internet company, for $187.5 million. This transaction marked the end of Western ownership and shifted control to a firm focused on emerging markets, particularly in and , where ICQ retained some nostalgic appeal. Mail.ru aimed to revitalize the service by integrating it into its ecosystem, including interoperability with its own Mail.ru Agent platform, allowing cross-communication between users without requiring dual accounts. Under Mail.ru's stewardship, ICQ received updates to enhance functionality, such as improved mobile support and multimedia features, positioning it as one of the more versatile legacy messengers by the mid-2010s. The company invested significantly in development, removing intrusive banner ads starting in May 2011 to prioritize over immediate monetization. However, these efforts occurred against a backdrop of intensifying competition from mobile-native applications like and Telegram, which offered seamless cross-platform synchronization, , and rapid innovation—areas where ICQ lagged due to its desktop-centric origins and slower adaptation to dominance. By 2016, Mail.ru executives acknowledged ICQ's challenges in capturing mobile market share, with product head Igor Yermakov noting the service's prior failure to pivot quickly enough from PC-based usage. A 2020 relaunch attempted to leverage heightened global interest in digital communication amid the COVID-19 pandemic, introducing "ICQ New" with refreshed interfaces and integration into Mail.ru's broader services like TamTam. Despite such initiatives, ICQ experienced prolonged stagnation, as user migration to ecosystem-locked platforms (e.g., Facebook Messenger) and privacy-focused alternatives eroded its relevance, culminating in diminished active engagement and eventual de-listing from major app stores. Mail.ru's rebranding to VK Company in 2021 did not reverse this trajectory, with geopolitical tensions following Russia's 2022 invasion of Ukraine exacerbating operational constraints for a Russia-based service.

Shutdown and Final Operations (2024)

On May 24, 2024, VK, the Russian technology company that had owned ICQ since acquiring it through its Mail.ru Group subsidiary in 2010, announced the discontinuation of the service effective June 26, 2024. The announcement appeared on ICQ's official website without specifying reasons for the shutdown, though VK had previously indicated a strategic shift toward consolidating its messaging . In the lead-up to the closure, ICQ's website displayed a notice directing users to migrate to VK's alternative platforms, including VK Messenger and VK Teams (formerly Mail.ru Agent), for continued communication. No data export options or account preservation features were provided, rendering user contacts, chat histories, and unique ICQ numbers (UINs) inaccessible after shutdown. On June 26, 2024, ICQ ceased all operations, with the service displaying a message confirming it had "stopped working." Client applications across platforms, including desktop, mobile, and web versions, became non-functional, marking the end of the protocol's active support after nearly 28 years since its 1996 launch. Third-party clients relying on ICQ servers were similarly affected, as the was fully decommissioned without any transitional to other networks.

Technical Architecture and Features

Core Messaging Protocol and Infrastructure

ICQ's core messaging protocol was a , binary-based system developed by Mirabilis, relying on a client-server model for presence detection and message routing, augmented by direct connections for certain interactions. Clients initiated communication via UDP packets to central authorization and (Basic Oscar Service) servers, typically on 4000 for and presence updates, enabling real-time status broadcasting to contacts without persistent TCP sessions for lightweight operations. This UDP-centric approach for server interactions minimized latency for "who's online" queries and short messages, while TCP was reserved for reliable delivery in client-to-client exchanges, such as typed messages, sharing, file transfers, and multi-user chats, where IP addresses and ports were exchanged via the server to establish direct links. The protocol's packet format included fixed headers with version identifiers (e.g., 0x0005 in early schemes), sequence numbers for ordering, and variable-length payloads encoded in a non-textual binary structure, lacking initial and thus exposing to . The infrastructure underpinning this protocol featured a centralized cluster of servers managed by Mirabilis, initially hosted in , designed for horizontal scalability through load-balanced nodes handling authentication, directory services, and message proxying. This architecture allowed rapid growth to millions of users by , as servers could distribute presence lists and route undelivered messages stored temporarily in server-side queues until recipients came online. Post-acquisition by in , the backend evolved to integrate with AOL's global data centers, adopting elements of the OSCAR protocol (Open System for CommunicAtion in Realtime) for compatibility with AIM, which standardized binary TLV (Type-Length-Value) encoding for extensible packets across services like (FLAP channels) and messaging (SNAC packets). However, the core remained non-interoperable with open standards like IRC or XMPP, prioritizing proprietary efficiency over federation, which facilitated features like invisible mode and away messages but invited security vulnerabilities from unencrypted UDP broadcasts. Under later ownership by Mail.ru (from 2010), the protocol shifted to the WIM (Web Instant Messenger) framework around 2010 to supplant OSCAR, introducing HTTP-based tunneling for firewall traversal and simplified XML-like payloads, though retaining client-server dependency for core routing. This evolution addressed scalability for mobile clients but preserved the centralized infrastructure, with servers increasingly consolidated in Russian data centers, contributing to eventual amid concerns. The absence of throughout most versions underscored a focused on over , as evidenced by early exploits like packet spoofing.

User Identification System (UIN) and Authentication

The ICQ user identification system centers on the Unique Identification Number (UIN), a unique, sequentially assigned numerical identifier granted to each user at the time of account registration. UINs were distributed starting from low numbers—such as those in the single or low double digits for the earliest registrants—and incremented thereafter, enabling users to be distinctly identified, searched, and contacted across the network. This permanent identifier facilitated core functions like adding contacts via direct UIN entry and served as the foundational element for user discovery in the absence of advanced search features in early versions. Authentication in ICQ required users to provide their UIN paired with a user-selected , which the client software transmitted to ICQ servers for verification during . The process involved establishing a TCP/IP connection, where the client sent the UIN, an encrypted form of the password, along with details such as the client's and reserved port. Servers compared these credentials against stored account data; successful validation authorized access to services like the Basic Oscar Service (BOS) in the OSCAR protocol, enabling session establishment and feature utilization. Early implementations lacked robust client-server , relying primarily on password protection, which exposed the system to risks such as spoofing if credentials were intercepted or guessed. Password management included recovery options tied to a pre-set secret question or the user's primary , allowing resets without direct server intervention in some cases. However, vulnerabilities periodically undermined security; for instance, in August 1998, a flaw permitted unauthorized logins using passwords exceeding eight characters on non-Windows platforms due to improper handling. Desirable low or patterned UINs (e.g., palindromes or phone-like sequences) became tradable commodities, sometimes through unauthorized means, highlighting the identifier's perceived value but also incentivizing account compromises. Under later ownership by Mail.ru Group (from 2010), the protocol shifted from OSCAR to the WIM protocol, which maintained UIN-password as the default but introduced alternatives like phone number authentication supplemented by verification codes for added two-factor elements. This evolution aimed to enhance and amid growing threats like malware-driven credential theft, though legacy UIN dependency persisted for compatibility with older clients and networks.

Evolving Features: From Basic Chat to Multimedia (ICQ New and Beyond)

ICQ initially launched in November 1996 with core features centered on real-time , including one-on-one chats, multi-user chat rooms, buddy lists for tracking online status, and direct file transfers supporting resumable sessions. These capabilities marked an advancement over earlier IRC-based systems by introducing a graphical client with searchable user directories and asynchronous offline message delivery, enabling communication without requiring both parties to be online simultaneously. As ICQ expanded under AOL's ownership from 1998, features evolved to include integration for mobile notifications and alerts for missed messages, broadening accessibility beyond desktop users. By 2004, the platform introduced video chat functionality, leveraging support for , which represented one of the earliest implementations of such in consumer . Voice chat capabilities were also added during this period, enhancing ICQ's VoIP elements and positioning it as a multifaceted communication tool amid growing adoption. The 2010 relaunch of ICQ New, following its acquisition by Digital Sky Technologies (later Mail.ru Group), shifted focus toward mobile-first multimedia experiences with ICQ 7, emphasizing real-time interactions beyond traditional text. This iteration introduced cloud-synchronized chat histories, expanded group chats supporting up to thousands of participants, audio messaging, and enhanced limits reaching 1 GB per transfer. Subsequent updates incorporated stickers, support, bots for automated interactions, and advanced video calling with features like screen sharing and call recording, adapting to ecosystems and competing with emerging apps like . Beyond ICQ New, later versions integrated social feeds, channels for discussions, and cross-platform compatibility, though development stagnated post-2010 amid changes, limiting further in areas like compared to contemporaries. By the , staples such as calls and voice notes became standard, but reliance on centralized servers exposed vulnerabilities, contributing to its eventual shutdown in June 2024 without significant protocol overhauls.

Client Software and Compatibility

Official Clients: Platforms and Versions

The official ICQ clients supported desktop platforms including Windows (from the initial 1996 release), macOS, and , with mobile apps for Android and developed later under VK ownership before their removal from respective app stores around 2022 in favor of VK's own messenger. A web client provided browser-based access, introduced by 2001 to enable server-stored contact lists independent of local installations. Desktop clients evolved through numbered versions, with ICQ 7 released in January 2010 as a major update expanding beyond to include VoIP and richer media handling on Windows and compatible systems. The final stable desktop version appeared in April 2023, supporting ongoing operations until the service shutdown on June 26, 2024. Earlier iterations, such as those under ownership, focused on Windows with periodic updates like ICQ 2000b introducing improved via protocol version 6. Mobile support began with ICQ for in 2009, bridging to smartphone-era clients for and Android that emphasized "ICQ New" features like multimedia sharing, though these lagged behind competitors in native app innovation and were phased out by 2022. Legacy mobile platforms including Java-enabled devices, , and received official clients during the 2000s but ceased updates well before the final years. Cross-platform compatibility relied on the core OSCAR-derived protocol, allowing official clients to interoperate while prioritizing Windows desktop as the primary development focus throughout most of ICQ's history.

Third-Party Clients and Interoperability Challenges

Third-party clients for ICQ proliferated in the early 2000s, driven by user dissatisfaction with the official client's resource demands, limited customization, and platform-specific constraints. Popular examples included QIP, a lightweight Russian-developed alternative that emphasized simplicity and gained widespread use in Eastern Europe as a de facto replacement for the official software, particularly with versions like QIP 2005. Open-source multi-protocol clients such as Pidgin (formerly Gaim) and Miranda IM also integrated ICQ support, enabling users to manage multiple networks from a single interface. These clients relied on community-driven reverse engineering of ICQ's proprietary OSCAR protocol, originally designed for AOL's AIM and adapted for ICQ starting around 2000, which allowed basic interoperability but introduced inherent fragility due to the closed nature of the specification. ICQ's deemed third-party clients a violation, as they circumvented official and feature controls, prompting periodic server-side interventions by and subsequent owners to disrupt compatibility. In 2001, AOL altered the protocol to exclude unofficial access, a tactic repeated in 2002 when ICQ fully transitioned to OSCAR, complicating ongoing reverse-engineering efforts and forcing developers to dissect encrypted packet structures via tools like network sniffers. These changes created acute hurdles, including authentication failures and message delivery breakdowns, as third-party implementations struggled to match evolving server expectations without official documentation. A notable escalation occurred on , 2008, when ICQ raised the minimum protocol version requirement, severing connections for clients like and Kopete until developers issued patches. On January 21, 2009, server blocks targeted unofficial clients from IP addresses in and , regions with high third-party adoption, further eroding reliability. Such disruptions demanded constant vigilance from maintainers, often exposing users to unverified code lacking timely security updates, while official responses emphasized protection against exploits prevalent in reverse-engineered versions. By December 2018, under VK ownership, ICQ explicitly discontinued support for legacy and unofficial applications, citing protocol deprecation and urging migration to the sanctioned client. These challenges—frequent obsolescence, development overhead for protocol dissection, and enforced silos—deterred long-term third-party viability, pushing users toward open-standard alternatives like XMPP-based systems that avoided lock-in. Unofficial clients, while innovative, amplified risks such as spoofing vulnerabilities inherent to the reverse-engineered OSCAR, where incomplete fidelity to server logic enabled sequence number overflows and unauthorized access attempts. Ultimately, the lack of standardized stifled ecosystem diversity, contrasting with contemporaneous protocols that embraced for sustained third-party innovation.

Controversies

ICQ maintained a restrictive stance toward unofficial clients throughout much of its , prioritizing control over the protocol to ensure security, feature consistency, and revenue from official software. Under AOL's ownership from to 2010, the company adopted an aggressive approach, repeatedly altering server protocols to disrupt third-party compatibility and discourage . In July 2008, for example, ICQ implemented server-side changes that rendered many unofficial clients, such as Kopete, inoperable by rejecting connections from outdated or non-compliant software versions. After Mail.Ru Group's acquisition in , efforts shifted temporarily toward accommodation. The new owner introduced a licensing framework to formalize and regulate unofficial clients, framing it as a core developmental priority to integrate developers while mitigating risks like protocol vulnerabilities exploited in unofficial implementations. This agreement allowed select third-party developers to access official APIs under terms that aligned with ICQ's evolving infrastructure, though adoption remained limited amid ongoing technical hurdles. Subsequent ownership by VK, starting in 2014, reversed this openness, culminating in outright disablement of third-party support. Beginning in December 2018, ICQ severed compatibility with various unofficial clients, extending to widespread blocks by early 2019, including . On April 1, 2019, the service fully discontinued with external applications, directly affecting multi-protocol clients like Trillian and citing security concerns over unverified implementations. This policy aligned with broader industry trends toward closed ecosystems but accelerated ICQ's user erosion, as enthusiasts reliant on customized clients migrated elsewhere. ICQ pursued no major lawsuits against third-party developers; enforcement relied predominantly on technical barriers, such as failures and protocol obfuscation, rather than courtroom actions. Critics argued these measures stifled innovation and , while proponents, including ICQ's operators, emphasized protection against exploits inherent in unauthorized software lacking official patches.

Data Cooperation with Russian Authorities Under VK Ownership

Mail.ru Group, now known as VK, acquired ICQ from in 2010, integrating the service into its portfolio of Russian-based internet platforms. This shift placed ICQ under Russian jurisdiction, subjecting its operations to . Russian No. 152-FZ, governing processing, was amended by No. 242-FZ on July 22, 2014, requiring operators to store and process of Russian citizens using databases physically located within to ensure accessibility for regulatory oversight. Subsequent legislation intensified data retention obligations applicable to messaging services. The Yarovaya package, enacted on July 22, 2016, compels communication providers—including internet-based platforms like ICQ—to retain metadata of user communications for three years and the content of messages, calls, and other electronic exchanges for six months. This must be stored in a manner enabling prompt decryption and handover to security services, such as the (FSB), upon official request, without prior judicial warrant in many cases. VK, registered as an organizer of information dissemination under Federal Law No. 149-FZ, complies by maintaining infrastructure for such retention, extending to ICQ's user base integrated with VK's ecosystem. VK's explicitly affirm adherence to these laws, permitting disclosure of user data—including from ICQ—to state authorities for , , or legal compliance purposes. While no public disclosures detail specific ICQ data handovers, the legal framework ensures authorities' technical access via systems like (System for Operative Investigative Activities), which mandates installation of monitoring equipment at providers' facilities. This compliance, driven by Russia's sovereign and counter-terrorism policies, contrasts with pre-acquisition operations under U.S. ownership, where such mandatory state access was absent.

Incidents of Platform Misuse for Child Exploitation

In the late and early , ICQ's real-time chat functionality and unique user identification numbers (UINs), which enabled pseudonymous interactions without mandatory real-name verification, facilitated misuse by individuals seeking to groom minors or distribute child sexual abuse material (CSAM). reports and court records document ICQ as a vector for such activities, particularly before the widespread adoption of moderated social networks, due to its global reach and lack of built-in content filtering at the time. A notable early incident occurred in 1999, when John Wingfield, a 56-year-old English Catholic teaching at a girls' in Kingston, , downloaded CSAM through an ICQ populated by dozens of pedophiles. Wingfield stored the illicit images on a school computer, leading to his ; he received two years' and placement on the UK's national sex offenders register. Police investigator PC Neal Ysart noted that ICQ users often harbored a false sense of security, contributing to the platform's appeal for such networks. U.S. federal and state cases similarly highlight ICQ's role in predator communications. In State v. Townsend (2002), Washington authorities used automatically recorded ICQ messages as against a defendant charged with CSAM possession and related offenses, demonstrating how the platform's default logging features inadvertently aided investigations. Multiple prosecutions, including a 2010 federal sentencing in for CSAM distribution, referenced ICQ contacts with international users as part of offenders' networks for sharing material. Expert testimony before and academic analyses from the era underscore ICQ's exploitation for "lolita business"—slang for trading—via chat lines, often leading to arrests through undercover operations posing as interested parties. The U.S. Department of Justice's 2008 National Strategy for Child Exploitation Prevention identified ICQ alongside other early protocols like IRC as common tools for online solicitation and grooming, citing its ease of anonymous exchanges. Such misuse declined with ICQ's user base erosion post-2005, as predators migrated to emerging platforms with or larger features, though isolated cases persisted into the .

Broader Security and Privacy Criticisms

ICQ has faced longstanding criticisms for inadequate security measures, particularly in its early iterations under Mirabilis and ownership, where instant messages were transmitted without , rendering them vulnerable to by network intermediaries or man-in-the-middle attacks. A 2001 analysis highlighted that ICQ's protocol lacked safeguards for and , allowing unauthorized access to stored conversations on client devices. Even later versions, including ICQ New, explicitly warned users that communications were unencrypted and could be routed through servers in multiple jurisdictions, exposing content to potential or third-party logging without user consent. Multiple software vulnerabilities exacerbated these risks, enabling remote code execution and system compromise. In May 2003, security firm Core Security Technologies identified two critical flaws in ICQ clients—one in the reception feature and another in banner ad handling—that permitted attackers to execute arbitrary code on victims' machines via malicious messages or ads, potentially leading to full control over infected systems. These issues stemmed from buffer overflows and insufficient input validation, common in the era's messaging software but unaddressed promptly in ICQ, drawing rebukes from researchers for prioritizing feature expansion over robust defenses. Server-side breaches further underscored operational weaknesses. In June 2001, hackers from the group "Men in Hack" infiltrated 's ICQ web servers, defacing the homepage and compromising search functionalities, though claimed no user data was exfiltrated; the incident exposed lapses in server hardening and perimeter defenses. Account hijackings also proliferated, with reports of UIN takeovers used for ransom demands, as in a 2001 case where a consultant's account was seized and held until payment was negotiated, highlighting flaws in the system's recovery and verification processes. advocates criticized ICQ's default visibility settings, which made user details like status and contact lists publicly discoverable via UIN searches, facilitating , spam, and unauthorized profiling without granular controls. Critics, including security analysts, have attributed these persistent shortcomings to ICQ's legacy , designed in without modern cryptographic standards, and a slow pivot to amid ownership transitions. The platform's warnings against using it for confidential matters—issued in and incident responses—underscored an implicit acknowledgment of these risks, yet implementation of remained absent, contrasting sharply with contemporaries like later iterations of competitors that adopted it. This combination of unencrypted transmission, exploitable code, and breach history positioned ICQ as a cautionary example in early discourse.

Impact and Legacy

Innovations and Achievements in Early Instant Messaging

ICQ, developed by the Israeli startup Mirabilis and released in November 1996, marked the advent of standalone software, decoupling real-time text communication from proprietary online services like or . This client-server architecture enabled connections via the , supporting features such as immediate delivery and presence detection, which contrasted with earlier IRC-based or email-dependent systems. Central to ICQ's innovation was the introduction of the buddy list, a dynamic contact roster displaying real-time online status for selected users, allowing proactive notifications upon a contact's availability. Complementing this, each user received a permanent Unique Identification Number (UIN)—such as the example 6377119—serving as a searchable identifier independent of changeable usernames, streamlining connections across global networks. Further advancements included multi-user chat rooms for group discussions, direct file transfers with resumable capabilities, and asynchronous offline messaging, where undelivered messages queued for later receipt. These elements, built rapidly in under two months by a small team, prioritized low-bandwidth efficiency suitable for dial-up connections. ICQ's achievements underscored its transformative impact, rapidly scaling to over 850,000 users within its first year through word-of-mouth adoption, particularly among gamers and international communities. By spring 2001, registrations exceeded 100 million, establishing it as the dominant early instant messenger and catalyzing the proliferation of rivals like (launched 1997) and . Its open-protocol influence extended to experiments and feature standardization, such as status indicators and searchable directories, which later permeated platforms including Yahoo! Messenger and even modern apps like . Mirabilis' sale to for $407 million in 1998 validated ICQ's commercial viability, though subsequent neglect highlighted tensions between innovation and corporate integration.

Cultural Role in Global Online Socialization

ICQ facilitated early global online socialization by providing one of the first accessible platforms for real-time cross-border communication, launched on November 15, 1996, by Israeli developers at Mirabilis. With over 100 million registered users at its peak in the early , the service's core features—such as unique user identification numbers (UINs) for easy sharing, customizable profiles, online status visibility, and searchable directories—enabled spontaneous connections beyond local networks, particularly in gaming communities like MUDs and interest-based chat rooms. These tools allowed users, often teenagers and young adults, to discover and engage with individuals worldwide, fostering friendships and exchanges in an era when physical travel and alternative digital options were limited. The platform's global reach amplified its cultural influence, achieving widespread adoption in diverse regions including , where it retained millions of users into the 2010s as a primary social tool amid slower development of local competitors. In emerging markets, ICQ's simplicity and multimedia support democratized socialization, enabling interactions that bridged cultural gaps through shared interests rather than geography, such as coordinating online gaming or casual conversations. Its iconic "uh-oh" alert sound and pop-up notifications became embedded in users' daily experiences, symbolizing the novelty of persistent online presence and contributing to a shared generational for unfiltered digital bonding. ICQ also spurred linguistic and communicative adaptations in multicultural contexts, as evidenced by its role in hybrid English-Cantonese discourse among users, where private chats generated novel varieties that reflected evolving social norms in bilingual environments. Among adolescents in the early 2000s, ICQ supported friendship development through informal, low-pressure exchanges, often preferred over alternatives like for its immediacy and features. By emphasizing user-initiated discovery—"I Seek You"—ICQ normalized proactive global networking, influencing subsequent platforms' design while highlighting early internet socialization's emphasis on individual agency over structured social graphs.

Factors in Decline and Influence on Successors

ICQ's decline accelerated after its acquisition by in June 1998 for $407 million, as prioritized its own AOL Instant Messenger (AIM), launched in 1997, which rapidly gained dominance in the United States through aggressive marketing and integration with 's dial-up service. This shift fragmented the instant messaging market, with competing closed-protocol services like Microsoft's MSN Messenger (1999) and Yahoo! Messenger drawing users away via proprietary ecosystems tied to email and web portals, undermining ICQ's early network effects despite its initially . By the early 2000s, ICQ's user base, which had peaked at over 100 million registered accounts, began eroding as these rivals offered fresher interfaces and better cross-platform support. The rise of mobile internet and social networking platforms in the late 2000s further diminished ICQ's relevance, as services like Chat (2008) and early mobile apps integrated messaging into broader social graphs, prioritizing seamless access over desktop-centric clients. ICQ struggled with adaptation, retaining outdated features amid growing spam, vulnerabilities—such as weak and susceptibility to —and a failure to innovate for mobile ecosystems, leading to its removal from major app stores by under VK ownership. VK, which acquired ICQ from in 2010 for an undisclosed sum, redirected resources to its own platforms, culminating in the service's shutdown announcement on May 24, 2024, with operations ceasing on June 26, 2024, due to insufficient active users and unsustainable maintenance costs. Despite its fall, ICQ profoundly shaped successor instant messaging protocols and applications by establishing core paradigms like unique persistent user identifiers (UINs), dynamic buddy lists for real-time presence detection, searchable directories, and asynchronous offline messaging, which AIM explicitly emulated upon release to capitalize on ICQ's proven model. These elements influenced MSN Messenger's away statuses and file-sharing capabilities, as well as Yahoo! Messenger's multi-user chats, fostering the standardized IM framework that later informed mobile-era apps such as WhatsApp's contact syncing and status indicators. ICQ's emphasis on cross-platform interoperability, though imperfect, prefigured federation attempts in later services, while its audio alerts and lightweight client design echoed in the user-friendly evolution of Telegram and Signal, underscoring its role in normalizing real-time digital socialization.

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