Ransomware
Ransomware
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Ransomware

Ransomware is a type of malware that encrypts the victim's personal data until a ransom is paid. Difficult-to-trace digital currencies such as paysafecard or Bitcoin and other cryptocurrencies are commonly used for the ransoms, making tracing and prosecuting the perpetrators difficult. Sometimes the original files can be retrieved without paying the ransom due to implementation mistakes, leaked cryptographic keys or a complete lack of encryption in the ransomware.

Ransomware attacks are typically carried out using a Trojan disguised as a legitimate file that the user is tricked into downloading or opening when it arrives as an email attachment. However, one high-profile example, the WannaCry worm, traveled automatically between computers without user interaction.

Starting as early as 1989 with the first documented ransomware known as the AIDS trojan, the use of ransomware scams grew internationally. There were 181.5 million ransomware attacks worldwide in the first six months of 2018, 229% more than the first six months of 2017. In June 2014, security software company McAfee released data showing that it had collected more than double the number of ransomware samples that quarter than it had in the same quarter the previous year. CryptoLocker was particularly successful, procuring an estimated US$3 million before it was taken down by authorities, and CryptoWall was estimated by the US Federal Bureau of Investigation (FBI) to have accrued over US$18 million by June 2015. In 2020, the US Internet Crime Complaint Center (IC3) received 2,474 complaints identified as ransomware, with adjusted losses of over $29.1 million. The losses could exceed this amount, according to the FBI. Globally, according to Statista, there were about 623 million ransomware attacks in 2021, and 493 million in 2022.

Ransomware payments were estimated at $1.1bn in 2019, $999m in 2020, a record $1.25bn in 2023, and a sharp drop to $813m in 2024, attributed to non-payment by victims and action by law enforcement.

The concept of file-encrypting ransomware was invented and implemented by Young and Yung at Columbia University and was presented at the 1996 IEEE Security & Privacy conference. It is called cryptoviral extortion and it was inspired by the fictional facehugger in the movie Alien. Cryptoviral extortion is the following three-round protocol carried out between the attacker and the victim.

The symmetric key is randomly generated and will not assist other victims. At no point is the attacker's private key exposed to victims and the victim need only send a very small ciphertext (the encrypted symmetric-cipher key) to the attacker.

Ransomware attacks are typically carried out using a Trojan, entering a system through, for example, a malicious attachment, an embedded link in a phishing email, or a vulnerability in a network service. The program then runs a payload, which locks the system in some fashion, or claims to lock the system but does not (e.g., a scareware program). Payloads may display a fake warning purportedly by an entity such as a law enforcement agency, falsely claiming that the system has been used for illegal activities, contains content such as pornography and "pirated" media.

Some payloads consist simply of an application designed to lock or restrict the system until payment is made, typically by setting the Windows Shell to itself, or even modifying the master boot record and/or partition table to prevent the operating system from booting until it is repaired. The most sophisticated payloads encrypt files, with many using strong encryption to encrypt the victim's files in such a way that only the malware author has the needed decryption key.

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