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In computing, a Trojan horse, or Trojan, 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 e-mail 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 and worms, Trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves.[7]

Origin of the conceptEdit

This terminology occurred for the first time in a US Air Force report in 1974 on the analysis of vulnerability in computer systems.[8] It was made popular by Ken Thompson in his 1983 Turing Award acceptance lecture "Reflections on Trusting Trust",[9] 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 Trojan horses in a report on the security of Multics of which he was unfortunately unable to find a reference. However Paul Karger and Roger Schell affirm that this is their above cited report.[10][8][11]

Malicious usesEdit

Trojan Viruses, in this way, may require interaction with a malicious controller (not necessarily distributing the Trojan) to fulfil their purpose. It is possible for those involved with Trojans to scan computers on a network to locate any with a Trojan installed, which the hacker can then control.[12]

Some Trojans take advantage of a security flaw in older versions of Internet Explorer and Google Chrome to use the host computer as an anonymizer proxy to effectively hide Internet usage,[13] enabling the controller to use the Internet for illegal purposes while all potentially incriminating evidence indicates the infected computer or its IP address. The host's computer may or may not show the internet history of the sites viewed using the computer as a proxy. The first generation of anonymizer Trojan horses tended to leave their tracks in the page view histories of the host computer. Later generations of the Trojan tend to "cover" their tracks more efficiently. Several versions of Sub7 have been widely circulated in the US and Europe and became the most widely distributed examples of this type of Trojan.[12]

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 examplesEdit

Private and governmentalEdit

Publicly availableEdit

Detected by security researchersEdit

See alsoEdit

External linksEdit

  • "CERT Advisory CA-1999-02 Trojan Horses" (PDF). Carnegie Mellon University Software Engineering Institute. Archived from the original on July 17, 2001. Retrieved September 15, 2019.


  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.
  2. ^ "Trojan Horse Definition". Retrieved April 5, 2012.
  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. ^ "What is the difference between viruses, worms, and Trojans?". Symantec Corporation. Retrieved January 10, 2009.
  7. ^ "VIRUS-L/comp.virus Frequently Asked Questions (FAQ) v2.00 (Question B3: What is a Trojan Horse?)". October 9, 1995.
  8. ^ a b Karger, P.A.; Schell, R.R. (June 1974), "Multics Security Evaluation: Vulnerability Analysis , ESD-TR-74-193" (PDF), HQ Electronic Systems Division: Hanscom AFB, MA, II
  9. ^ Ken Thompson (1984). "Reflection on Trusting Trust". Commun. ACM. 27 (8): 761–763. doi:10.1145/358198.358210..
  10. ^ Paul A. Karger; Roger R. Schell (2002), "Thirty Years Later: Lessons from the Multics Security Evaluation" (PDF), ACSAC: 119–126
  11. ^ 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
  12. ^ a b Jamie Crapanzano (2003): "Deconstructing SubSeven, the Trojan Horse of Choice", SANS Institute, Retrieved on 2009-06-11
  13. ^ Vincentas (July 11, 2013). "Trojan Horse in". Spyware Loop. Retrieved July 28, 2013.
  14. ^ a b Basil Cupa, Trojan Horse Resurrected: On the Legality of the Use of Government Spyware (Govware), LISS 2013, pp. 419–428
  15. ^ "Dokument nicht gefunden!". Federal Department of Justice and Police. Archived from the original on May 6, 2013.
  16. ^ "Swiss coder publicises government spy Trojan –". Retrieved January 26, 2014.
  17. ^ "German federal police use Trojan virus to evade phone encryption". DW. Retrieved April 14, 2018.
  18. ^ Archived August 8, 2009, at the Wayback Machine Malware and Spam Survey
  19. ^ Datta, Ganesh (August 7, 2014). "What are Trojans?". SecurAid.
  20. ^ "Mega-Panzer".
  21. ^ "Mini-Panzer".
  22. ^ "Trojanized adware family abuses accessibility service to install whatever apps it wants – Lookout Blog".
  23. ^ "Shedun trojan adware is hitting the Android Accessibility Service – TheINQUIRER". November 20, 2015.
  24. ^ "Lookout discovers new trojanized adware; 20K popular apps caught in the crossfire – Lookout Blog".
  25. ^ "Shuanet, ShiftyBug and Shedun malware could auto-root your Android". November 5, 2015.
  26. ^ Times, Tech (November 9, 2015). "New Family of Android Malware Virtually Impossible To Remove: Say Hello To Shedun, Shuanet And ShiftyBug".
  27. ^ "Android adware can install itself even when users explicitly reject it". November 19, 2015.