Trojan horse (computing)

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In computing, a Trojan horse[a] (or simply trojan)[b] is any malware which misleads users of its true intent. The term is derived from the Ancient Greek story of the deceptive Trojan Horse that led to the fall of the city of Troy.[1][2][3][4][5]

Trojans are generally spread by some form of social engineering, for example where a user is duped into executing an email attachment disguised to appear not suspicious, (e.g., a routine form to be filled in), or by clicking on some fake advertisement on social media or anywhere else. Although their payload can be anything, many modern forms act as a backdoor, contacting a controller which can then have unauthorized access to the affected computer.[6] Trojans may allow an attacker to access users' personal information such as banking information, passwords, or personal identity. It can also delete a user's files or infect other devices connected to the network.Ransomware attacks are often carried out using a trojan.

Unlike computer viruses, worms, and rogue security software, trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves.[7]

Origin of the concept

It's not clear where or when the concept, and this term for it, was first used, but by 1971 the first Unix manual assumed its readers knew both:[8]

Also, one may not change the owner of a file with the set—user—ID bit on, otherwise one could create Trojan Horses able to misuse other’s files.

Another early reference is in a US Air Force report in 1974 on the analysis of vulnerability in the Multics computer systems.[9]

It was made popular by Ken Thompson in his 1983 Turing Award acceptance lecture "Reflections on Trusting Trust",[10] subtitled: To what extent should one trust a statement that a program is free of Trojan horses? Perhaps it is more important to trust the people who wrote the software. He mentioned that he knew about the possible existence of trojans from a report on the security of Multics.[11][12]

An early example of a trojan could be found on the UCLA DEC-10 in the late 1970s. Games such as ADVENT, a room to room adventure game, and WARGAM, a thermonuclear destruction game were readily available on the system. Users interested in finding more games to play could also find a program named GALAXY. When you executed this program it would create hundreds of randomly named files in your storage space. The random names prevented you from using wildcards to delete the files, they would have to be deleted one at a time if you wanted to keep any other files in your space.

Malicious uses

Once installed, trojans may perform a range of malicious actions. Many tend to contact one or more Command and Control (C2) servers across the Internet and await instruction. Since individual trojans typically use a specific set of ports for this communication, it can be relatively simple to detect them. Moreover, other malware could potentially "take over" the trojan, using it as a proxy for malicious action.[13]

In German-speaking countries, spyware used or made by the government is sometimes called govware. Govware is typically a Trojan software used to intercept communications from the target computer. Some countries like Switzerland and Germany have a legal framework governing the use of such software.[14][15] Examples of govware trojans include the Swiss MiniPanzer and MegaPanzer[16] and the German "state trojan" nicknamed R2D2.[14] German govware works by exploiting security gaps unknown to the general public and accessing smartphone data before it becomes encrypted via other applications.[17]

Due to the popularity of botnets among hackers and the availability of advertising services that permit authors to violate their users' privacy, trojans are becoming more common. According to a survey conducted by BitDefender from January to June 2009, "trojan-type malware is on the rise, accounting for 83% of the global malware detected in the world." Trojans have a relationship with worms, as they spread with the help given by worms and travel across the internet with them.[18] BitDefender has stated that approximately 15% of computers are members of a botnet, usually recruited by a trojan infection.[19]

Notable examples

Private and governmental

Publicly available

  • EGABTR – late 1980s
  • Netbus – 1998 (published)[20]
  • Sub7 by Mobman – 1999 (published)
  • Back Orifice – 1998 (published)
  • Y3K Remote Administration Tool by E&K Tselentis – 2000 (published)
  • Beast – 2002 (published)
  • Bifrost trojan – 2004 (published)
  • DarkComet – 2008-2012 (published)
  • Blackhole exploit kit – 2012 (published)
  • Gh0st RAT – 2009 (published)
  • MegaPanzer BundesTrojaner – 2009 (published)[21][22]
  • MEMZ by Leurak – 2016 (published)

Detected by security researchers

  • Twelve Tricks – 1990
  • Clickbot.A – 2006 (discovered)
  • Zeus – 2007 (discovered)
  • Flashback trojan – 2011 (discovered)
  • ZeroAccess – 2011 (discovered)
  • Koobface – 2008 (discovered)
  • Vundo – 2009 (discovered)
  • Meredrop – 2010 (discovered)
  • Coreflood – 2010 (discovered)
  • Tiny Banker Trojan – 2012 (discovered)
  • Shedun Android malware – 2015 (discovered)[23][24][25][26][27][28]

Orthographic note

The term "trojan horse" in computing is derived from the legendary Trojan Horse; itself named after Troy. For this reason "Trojan" is often capitalized. However, while style guides and dictionaries differ, many suggest a lower case "trojan" for normal use.[29][30] That is the approach taken in this article - apart from when first introducing the word and its derivation.

See also

  • Computer security
  • Cyber spying
  • Dancing pigs
  • Exploit (computer security)
  • Industrial espionage
  • Principle of least privilege
  • Privacy-invasive software
  • Remote administration
  • Remote administration software
  • Reverse connection
  • Rogue security software
  • Scammers
  • Technical support scam – unsolicited phone calls from a fake "tech support" person, claiming that the computer has a virus or other problems
  • Timeline of computer viruses and worms
  • Zombie (computer science)


  1. ^ Upper case is intentional here, please see the "Orthographic note" section, and the Talk page
  2. ^ Lower case is intentional here, please see the "Orthographic note" section , and the Talk page


  1. ^ Landwehr, Carl E.; Alan R. Bull; John P. McDermott; William S. Choi (1993). A taxonomy of computer program security flaws, with examples. DTIC Document. CiteSeerX . Retrieved April 5, 2012.
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  3. ^ "Trojan horse". Webopedia. Retrieved April 5, 2012.
  4. ^ "What is Trojan horse? – Definition from". Retrieved April 5, 2012.
  5. ^ "Trojan Horse: [coined By MIT-hacker-turned-NSA-spook Dan Edwards] N." Retrieved April 5, 2012.
  6. ^ "Difference between viruses, worms, and trojans". Symantec Security Center. Broadcom Inc. Archived from the original on August 19, 2013. Retrieved March 29, 2020.
  7. ^ "VIRUS-L/comp.virus Frequently Asked Questions (FAQ) v2.00 (Question B3: What is a Trojan Horse?)". October 9, 1995.
  8. ^ Thompsom, K. "UNIX PROGRAMMER'S MANUAL, November 3, 1971" (PDF). Retrieved March 28, 2020.
  9. ^ Karger, P.A.; Schell, R.R., "Multics Security Evaluation: Vulnerability Analysis , ESD-TR-74-193" (PDF), HQ Electronic Systems Division: Hanscom AFB, MA, II
  10. ^ Ken Thompson (1984). "Reflection on Trusting Trust". Commun. ACM. 27 (8): 761–763. doi:..
  11. ^ Paul A. Karger; Roger R. Schell (2002), "Thirty Years Later: Lessons from the Multics Security Evaluation" (PDF), ACSAC: 119–126
  12. ^ Karger et Schell wrote that Thompson added this reference in a later version of his Turing conference: Ken Thompson (November 1989), "On Trusting Trust.", Unix Review, 7 (11): 70–74
  13. ^ Crapanzano, Jamie (2003). Deconstructing SubSeven, the Trojan Horse of Choice (Report). SANS Institute. Retrieved May 10, 2021.
  14. ^ a b Basil Cupa, Trojan Horse Resurrected: On the Legality of the Use of Government Spyware (Govware), LISS 2013, pp. 419–428
  15. ^ "Häufig gestellte Fragen (Frequently Asked Questions)". Federal Department of Justice and Police. Archived from the original on May 6, 2013.
  16. ^ Dunn, John (August 27, 2009). "Swiss coder publicises government spy Trojan". TechWorld. Archived from the original on January 26, 2014. Retrieved January 10, 2021.
  17. ^ "German federal police use trojan virus to evade phone encryption". DW. Retrieved April 14, 2018.
  18. ^ "BitDefender Malware and Spam Survey finds E-Threats Adapting to Online Behavioral Trends". BitDefender. Archived from the original on August 8, 2009. Retrieved March 27, 2020.
  19. ^ Datta, Ganesh (August 7, 2014). "What are Trojans?". SecurAid. Archived from the original on August 12, 2014. Retrieved March 27, 2020.
  20. ^ Seth, Kulakow (1998). "Is it still a Trojan horse or an Actual Valid Remote Control Administration Tool?" (Report). SANS Institute. Retrieved May 10, 2021.
  21. ^ "Mega-Panzer".
  22. ^ "Mini-Panzer".
  23. ^ "Trojanized adware family abuses accessibility service to install whatever apps it wants – Lookout Blog".
  24. ^ Neal, Dave (November 20, 2015). "Shedun trojan adware is hitting the Android Accessibility Service". The Inquirer. Incisive Business Media. Archived from the original on November 22, 2015. Retrieved March 27, 2020.CS1 maint: unfit URL (link)
  25. ^ "Lookout discovers new trojanized adware; 20K popular apps caught in the crossfire – Lookout Blog".
  26. ^ "Shuanet, ShiftyBug and Shedun malware could auto-root your Android". November 5, 2015.
  27. ^ Times, Tech (November 9, 2015). "New Family of Android Malware Virtually Impossible To Remove: Say Hello To Shedun, Shuanet And ShiftyBug".
  28. ^ "Android adware can install itself even when users explicitly reject it". November 19, 2015.
  29. ^ "trojan". Collins Advanced Dictionary. Retrieved March 29, 2020.
  30. ^ "trojan horse". Microsoft Style Guide. Microsoft. Retrieved March 29, 2020.

External links

Edited: 2021-06-18 12:30:37