Ransomware is a class of malware which restricts access to the computer system that it infects, and demands a ransom paid to the creator of the malware in order for the restriction to be removed. Some forms of ransomware encrypt files on the system's hard drive (cryptoviral extortion), while some may simply lock the system and display messages intended to coax the user into paying.
While initially popular in Russia, the use of ransomware scams has grown internationally; in June 2013, security software vendor McAfee released data showing that it had collected over 250,000 unique samples of ransomware in the first quarter of 2013—more than double the number it had obtained in the first quarter of 2012.
Ransomware typically propagates as a trojan like a conventional computer worm, entering a system through, for example, a downloaded file or a vulnerability in a network service. The program will then run a payload: such as one that will begin to encrypt personal files on the hard drive. More sophisticated ransomware may hybrid-encrypt the victim's plaintext with a random symmetric key and a fixed public key. The malware author is the only party that knows the needed private decryption key. Some ransomware payloads do not use encryption. In these cases, the payload is simply an application designed to restrict interaction with the system, typically by setting the Windows Shell to itself, or even modifying the master boot record and/or partition table (which prevents the operating system from booting at all until it is repaired).
Ransomware payloads utilize elements of scareware to extort money from the system's user. The payload may, for example, display notices purportedly issued by companies or law enforcement agencies which falsely claim that the system had been used for illegal activities, or contains illegal content such as pornography and pirated software or media. Some ransomware payloads imitate Windows XP's product activation notices, falsely claiming that their computer's Windows installation is counterfeit or requires re-activation. These tactics coax the user into paying the malware's author to remove the ransomware, either by supplying a program which can decrypt the files, or by sending an unlock code that undoes the changes the payload has made. These payments are often delivered using either a wire transfer, premium-rate text messages, through an online payment voucher service such as Ukash or Paysafecard, or most recently, the digital currency Bitcoin.
The first known ransomware was the 1989 "AIDS" trojan (also known as "PC Cyborg") written by Joseph Popp, which triggered a payload claiming that the user's license to use a certain piece of software had expired, encrypted file names on the hard drive, and required the user to pay US$189 to "PC Cyborg Corporation" in order to unlock the system. Popp was declared mentally unfit to stand trial for his actions, but he promised to donate the profits from the malware to fund AIDS research. The notion of using public key cryptography for such attacks was introduced in 1996 by Adam L. Young and Moti Yung. The two believed that the AIDS trojan was ineffective due to its use of symmetric cryptography, and presented a proof-of-concept cryptovirus for the Macintosh SE/30 using RSA and TEA. Young and Yung referred to this attack as being "cryptoviral extortion", an overt attack that is part of a larger class of attacks in a field called cryptovirology, which encompasses both overt and covert attacks.
Examples of extortionate ransomware became prominent in May 2005. By mid-2006, worms such as Gpcode, TROJ.RANSOM.A, Archiveus, Krotten, Cryzip, and MayArchive began utilizing more sophisticated RSA encryption schemes, with ever-increasing key-sizes. Gpcode.AG, which was detected in June 2006, was encrypted with a 660-bit RSA public key. In June 2008, a variant known as Gpcode.AK was detected. Using a 1024-bit RSA key, it was believed to be large enough to be computationally infeasible to break without a concerted distributed effort.
Encrypting ransomware returned to prominence in late 2013 the propagation of worms such as CryptoLocker, CryptoLocker 2.0, and CryptoDefense (which, notably, contained a major design flaw that allowed the private key to be stored on the infected system in a user-retrievable location)—using the Bitcoin digital currency platform to collect ransom money. In December 2013, ZDNet estimated that between October 15 and December 18, the operators of CryptoLocker had procured about US$27 million from infected users.
In August 2010, Russian authorities arrested ten individuals connected to a ransomware worm known as WinLock. Unlike the previous Gpcode worms, WinLock did not use encryption. Instead, WinLock trivially restricted access to the system by displaying pornographic images, and asked users to send a premium-rate SMS (costing around US$10) to receive a code that could be used to unlock their machines. The scam hit numerous users across Russia and neighboring countries—reportedly earning the group over US$16 million.
In 2011, a ransomware worm imitating the Windows Product Activation notice surfaced that informed users that a system's Windows installation would have to be re-activated due to "[being a] victim of fraud". An online activation option was offered (like the actual Windows activation process), but was unavailable, requiring the user to call one of six international numbers to input a 6-digit code. While the malware claimed that this call would be free, it was routed through a rogue operator in a country with high international phone rates, who placed the call on hold, causing the user to incur large long distance charges.
In February 2013, a ransomware worm based on the Stamp.EK exploit kit surfaced; the malware was distributed via sites hosted on the project hosting services SourceForge and GitHub that claimed to offer "fake nude pics" of celebrities. In July 2013, an OS X-specific ransomware worm surfaced, which displays a web page that accuses the user of downloading pornography. Unlike its Windows-based counterparts, it does not block the entire computer, but simply exploits the operation of the web browser itself to frustrate attempts to close the page through normal means.
In July 2013, a 21-year-old male from Virginia turned himself in to police after receiving ransomware containing a fake FBI warning accusing him of possessing child pornography. After an investigation, it was discovered that the user's computer, coincidentally, did contain pornographic photographs of underaged females, with whom he had conducted inappropriate communications. He was charged with possessing child pornography and child sexual abuse.
In 2012, a major ransomware worm known as Reveton began to spread. Based on the Citadel trojan (which itself, is based on the Zeus trojan), its payload displays a warning purportedly from a law enforcement agency (leading to its nickname as the "police trojan"), claiming that the computer had been used for illegal activities, such as downloading pirated software or child pornography. The warning informs the user that to unlock their system, they would have to pay a fine using a voucher from an anonymous prepaid cash service such as Ukash or Paysafecard. To increase the illusion that the computer is being tracked by law enforcement, the screen also displays the computer's IP address, while some versions display footage from a computer's webcam to give the illusion that the user is being purportedly recorded as well.
Reveton initially began spreading in various European countries in early 2012. Variants were localized with templates branded with the logos of different law enforcement organizations based on the user's country; for example, variants used in the United Kingdom contained the branding of organizations such as the Metropolitan Police Service, the collection society PRS for Music (which specifically accused the user of illegally downloading music), and the Police National E-Crime Unit. In a statement warning the public about the malware, the Metropolitan Police clarified that they would never lock a computer in such a way as part of an investigation. When authorities do have suspicion that someone is downloading or uploading child pornography, they will not give the suspect a heads up, as that would give them time to flee or dispose of evidence.
In May 2012, Trend Micro threat researchers discovered templates for variations for the United States and Canada, suggesting that its authors may have been planning to target users in North America. By August 2012, a new variant of Reveton began to spread in the United States, claiming to require the payment of a $200 fine to the FBI using a MoneyPak card.
Encrypting ransomware reappeared in 2013 with a worm known as "CryptoLocker". Distributed either as an attachment to a malicious e-mail or as a drive-by download, CryptoLocker first attempts to connect to a command-and-control server, after which it generates a 2048-bit RSA public and private key pair, and uploads the key to the server. The malware then attempts to encrypt data on any local or network storage drive that the user can access using a 2048-bit RSA key, targeting files matching a whitelist of file extensions. While the public key is stored on the computer, the private key is stored on the command-and-control server; CryptoLocker demands a payment with either a MoneyPak card or Bitcoin to recover the key and begin decrypting files, and threatens to delete the private key if a payment is not received within 3 days. Due to the extremely large key size it uses, analysts and those affected by the worm have considered CryptoLocker to be extremely difficult to repair.
- Dunn, John E. "Ransom Trojans spreading beyond Russian heartland". TechWorld. Retrieved 10 March 2012.
- "New Internet scam: Ransomware...". FBI. Aug 9, 2012.
- "Citadel malware continues to deliver Reveton ransomware...". Internet Crime Complaint Center (IC3). Nov 30, 2012.
- "Update: McAfee: Cyber criminals using Android malware and ransomware the most". InfoWorld. Retrieved 16 September 2013.
- Young, A.; Moti Yung (1996). "Cryptovirology: extortion-based security threats and countermeasures". Proceedings 1996 IEEE Symposium on Security and Privacy. p. 129. doi:10.1109/SECPRI.1996.502676. ISBN 0-8186-7417-2.
- Adam Young (2005). "Building a Cryptovirus Using Microsoft's Cryptographic API". In Zhou, Jianying; Lopez, Javier. Information Security: 8th International Conference, ISC 2005 (Springer-Verlag). pp. 389–401.
- Young, Adam (2006). "Cryptoviral Extortion Using Microsoft's Crypto API: Can Crypto APIs Help the Enemy?". International Journal of Information Security (Springer-Verlag) 5 (2): 67–76.
- "Ransomware: Fake Federal German Police (BKA) notice". SecureList (Kaspersky Lab). Retrieved 10 March 2012.
- "And Now, an MBR Ransomware". SecureList (Kaspersky Lab). Retrieved 10 March 2012.
- "Police warn of extortion messages sent in their name". Helsingin Sanomat. Retrieved 9 March 2012.
- McMillian, Robert. "Alleged Ransomware Gang Investigated by Moscow Police". PC World. Retrieved 10 March 2012.
- "Ransomware squeezes users with bogus Windows activation demand". Computerworld. Retrieved 9 March 2012.
- Danchev, Dancho (2009-04-22). "New ransomware locks PCs, demands premium SMS for removal". ZDNet. Retrieved 2009-05-02.
- "Ransomware plays pirated Windows card, demands $143". Computerworld. Retrieved 9 March 2012.
- Cheng, Jacqui (2007-07-18). "New Trojans: give us $300, or the data gets it!". Ars Technica. Retrieved 2009-04-16.
- "You’re infected—if you want to see your data again, pay us $300 in Bitcoins". Ars Technica. Retrieved 23 October 2013.
- "CryptoDefense ransomware leaves decryption key accessible". Computerworld. IDG. Retrieved 7 April 2014.
- Kassner, Michael. "Ransomware: Extortion via the Internet". TechRepublic. Retrieved 10 March 2012.
- Schaibly, Susan (2005-09-26). "Files for ransom". Network World. Retrieved 2009-04-17.
- Leyden, John (2006-07-24). "Ransomware getting harder to break". The Register. Retrieved 2009-04-18.
- Naraine, Ryan (2008-06-06). "Blackmail ransomware returns with 1024-bit encryption key". ZDnet. Retrieved 2009-05-03.
- Lemos, Robert (2008-06-13). "Ransomware resisting crypto cracking efforts". SecurityFocus. Retrieved 2009-04-18.
- Krebs, Brian (2008-06-09). "Ransomware Encrypts Victim Files With 1,024-Bit Key". Washington Post. Retrieved 2009-04-16.
- "Kaspersky Lab reports a new and dangerous blackmailing virus". Kaspersky Lab. 2008-06-05. Retrieved 2008-06-11.
- "Cryptolocker 2.0 – new version, or copycat?". WeLiveSecurity. ESET. Retrieved 18 January 2014.
- "New CryptoLocker Spreads via Removable Drives". Trend Micro. Retrieved 18 January 2014.
- Violet Blue (December 22, 2013). "CryptoLocker's crimewave: A trail of millions in laundered Bitcoin". ZDNet. Retrieved 2013-12-23.
- Leyden, John. "Russian cops cuff 10 ransomware Trojan suspects". The Register. Retrieved 10 March 2012.
- "Criminals push ransomware hosted on GitHub and SourceForge pages by spamming ‘fake nude pics’ of celebrities". TheNextWeb. Retrieved 17 July 2013.
- "New OS X malware holds Macs for ransom, demands $300 fine to the FBI for ‘viewing or distributing’ porn". TheNextWeb. Retrieved 17 July 2013.
- "Man gets ransomware porn pop-up, goes to cops, gets arrested on child porn charges". Ars Technica. Retrieved 31 July 2013.
- "Fake cop Trojan 'detects offensive materials' on PCs, demands money". The Register. Retrieved 15 August 2012.
- "Reveton Malware Freezes PCs, Demands Payment". InformationWeek. Retrieved 16 August 2012.
- Dunn, John E. "Police alert after ransom Trojan locks up 1,100 PCs". TechWorld. Retrieved 16 August 2012.
- Constantian, Lucian. "Police-themed Ransomware Starts Targeting US and Canadian Users". PC World. Retrieved 11 May 2012.
- "Disk encrypting Cryptolocker malware demands $300 to decrypt your files". Geek.com. Retrieved 12 September 2013.
- "CryptoLocker attacks that hold your computer to ransom". The Guardian. Retrieved 23 October 2013.
- "Destructive malware "CryptoLocker" on the loose - here's what to do". Naked Security. Sophos. Retrieved 23 October 2013.
- Russinovich, Mark (7 Jan 2013). "Hunting Down and Killing Ransomware (Scareware)". Microsoft TechNet blog.