Botnet

A botnet is a group of Internet-connected devices, each of which runs one or more bots. Botnets can be used to perform distributed denial-of-service (DDoS) attacks, steal data, send spam, and allow the attacker to access the device and its connection. The owner can control the botnet using command and control (C&C) software. The word "botnet" is a portmanteau of the words "robot" and "network". The term is usually used with a negative or malicious connotation.

A botnet is a logical collection of Internet-connected devices, such as computers, smartphones or Internet of things (IoT) devices whose security have been breached and control ceded to a third party. Each compromised device, known as a "bot," is created when a device is penetrated by software from a malware (malicious software) distribution. The controller of a botnet is able to direct the activities of these compromised computers through communication channels formed by standards-based network protocols, such as Internet Relay Chat (IRC) and Hypertext Transfer Protocol (HTTP).

Operating, building, or using a botnet to access or control devices without their owners’ authorization is illegal in most jurisdictions and is regularly prosecuted as hacking, fraud, or related cyber-crime. Law enforcement and private parties also use legal tools to disrupt botnets, but those takedowns raise separate legal and constitutional issues.

Botnets are increasingly rented out by cyber criminals as commodities for a variety of purposes, including as booter/stresser services.

Botnet architecture has evolved over time in an effort to evade detection and disruption. Traditionally, bot programs are constructed as clients which communicate via existing servers. This allows the bot herder (the controller of the botnet) to perform all control from a remote location, which obfuscates the traffic. Many recent botnets now rely on existing peer-to-peer networks to communicate. These P2P bot programs perform the same actions as the client–server model, but they do not require a central server to communicate.

The first botnets on the Internet used a client–server model to accomplish their tasks. Typically, these botnets operate through Internet Relay Chat networks, domains, or websites. Infected clients access a predetermined location and await incoming commands from the server. The bot herder sends commands to the server, which relays them to the clients. Clients execute the commands and report their results back to the bot herder.

In the case of IRC botnets, infected clients connect to an infected IRC server and join a channel pre-designated for C&C by the bot herder. The bot herder sends commands to the channel via the IRC server. Each client retrieves the commands and executes them. Clients send messages back to the IRC channel with the results of their actions.

In response to efforts to detect and decapitate IRC botnets, bot herders have begun deploying malware on peer-to-peer networks. These bots may use digital signatures so that only someone with access to the private key can control the botnet, such as in Gameover ZeuS and the ZeroAccess botnet.