View source for Trojan horse (computing)

{{Short description|Type of malware}}
{{hatnote|For the horse for which these are named, see [[Trojan Horse]]. For other uses, see [[Trojan Horse (disambiguation)]].}}
<noinclude>{{Requested move notice|1=Trojan (computer security)|2=Talk:Trojan horse (computing)#Requested move 30 May 2026}}
</noinclude>{{Use mdy dates|date=May 2018}}
{{Computer hacking}}
In [[computing]], a '''trojan horse''' or '''trojan''' 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 (security)|social engineering]]. Although their payload can be anything, many modern forms act as a [[backdoor (computing)|backdoor]], contacting a controller who can then have unauthorized access to the affected device.<ref name="Broadcom2013" /> [[Ransomware]] attacks are often carried out using a trojan. Unlike [[computer virus]]es and [[Computer worm|worms]], trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves.<ref>{{Cite web
   |title = VIRUS-L/comp.virus Frequently Asked Questions (FAQ) v2.00 (Question B3: What is a Trojan Horse?)
   |url = http://faqs.cs.uu.nl/na-dir/computer-virus/faq.html
   |date = October 9, 1995
   |access-date = September 16, 2019
   |archive-date = August 5, 2020
   |archive-url = https://web.archive.org/web/20200805171304/https://faqs.cs.uu.nl/na-dir/computer-virus/faq.html
   |url-status = dead}}</ref> Trojan horses are named after the [[Trojan Horse]].<ref name="Gregg2015"/>

==Origins of the term==
The term is derived from the [[Ancient Greece|ancient Greek]] story of the deceptive [[Trojan Horse]] that led to the fall of the city of [[Troy]].<ref name="Gregg2015"/> 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.<ref>{{cite web
   |last1=Thompson
   |first1=Ken
   |last2=Ritchie
   |first2=Dennis M.
   |title=Unix Programmer's Manual, November 3, 1971
   |url=https://www.bell-labs.com/usr/dmr/www/man21.pdf
   |page = 5
   |quote = 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.
   |access-date=28 March 2020}}</ref> Another early reference is in a US Air Force report in 1974 on the analysis of vulnerability in the [[Multics]] computer systems.<ref name="Karger1974" />

The term "Trojan horse" was popularized by [[Ken Thompson]] in his 1983 [[Turing Award]] acceptance lecture "Reflections on Trusting Trust",<ref name="Thompson1984"/> 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.<ref name="Karger2002"/><ref>Karger and Schell wrote that Thompson added this reference in a later version of his Turing conference speech: {{Citation|author = Ken Thompson|title = On Trusting Trust.
|journal = Unix Review|date = November 1989|volume = 7|number = 11|pages = 70–74}}</ref>

===Capitalization===
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 guide]]s and dictionaries suggest a lower-case "trojan" for this technical use.<ref name="Collins2020"/><ref name="Microsoft2020"/>

==Behavior==
[[File:MiniPanzer 0.1 3.png|thumb|Screenshot of [[MiniPanzer and MegaPanzer|MiniPanzer]]]]
Once installed, trojans may perform a range of malicious actions. Many tend to contact one or more [[Botnet#Command and control|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.<ref name="Crapanzano2003"/>

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.<ref name="cupa">Basil Cupa, [http://www.zora.uzh.ch/81157/1/Cupa_Living_in_Surveillance_Societies_2012.pdf Trojan Horse Resurrected: On the Legality of the Use of Government Spyware (Govware)] {{Webarchive|url=https://web.archive.org/web/20140201190736/http://www.zora.uzh.ch/81157/1/Cupa_Living_in_Surveillance_Societies_2012.pdf |date=February 1, 2014 }}, LISS 2013, pp. 419–428</ref><ref>{{cite web
   |url=http://www.ejpd.admin.ch/content/ejpd/de/home/themen/sicherheit/ueberwachung_des_post-/faq_vuepf.faq_3.html
   |title=Häufig gestellte Fragen (Frequently Asked Questions)| publisher=Federal Department of Justice and Police
   |url-status=dead
   |archive-url=https://web.archive.org/web/20130506102113/http://www.ejpd.admin.ch/content/ejpd/de/home/themen/sicherheit/ueberwachung_des_post-/faq_vuepf.faq_3.html| archive-date=May 6, 2013}}</ref> Examples of govware trojans include the Swiss [[MiniPanzer and MegaPanzer]]<ref name="tech">{{cite web
   |last1=Dunn
   |first1=John
   |title=Swiss coder publicises government spy Trojan
   |url=http://news.techworld.com/security/3200593/swiss-coder-publicises-government-spy-trojan/
   |website=[[International Data Group|TechWorld]]
   |access-date=10 January 2021|archive-url=https://archive.today/20140126115729/http://news.techworld.com/security/3200593/swiss-coder-publicises-government-spy-trojan/
   |archive-date=26 January 2014
   |date=27 August 2009
   |url-status=dead}}{{cbignore|bot=InternetArchiveBot}}</ref> and the [[Staatstrojaner|German "state trojan" nicknamed R2D2]].<ref name="cupa"/> German govware works by exploiting security gaps unknown to the general public and accessing smartphone data before it becomes encrypted via other applications.<ref>{{Cite web
   |title = German federal police use trojan virus to evade phone encryption
   |url = http://www.dw.com/en/german-federal-police-use-trojan-virus-to-evade-phone-encryption/a-42328466
   |website = [[Deutsche Welle|DW]]
   |access-date = 2018-04-14}}</ref>

Due to the popularity of [[Botnet|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|BitDefender]] from January to June 2009, "Trojan-type malware is on the rise, accounting for 83% of the global malware detected in the world."<ref name="Bitdefender2009"/> BitDefender has stated that approximately 15% of computers are members of a botnet, usually recruited by a trojan infection.<ref name="Datta2014"/>

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.<ref>{{Cite journal |last1=Kanaker |first1=Hasan |last2=Karim |first2=Nader Abdel |last3=Awwad |first3=Samer A. B. |last4=Ismail |first4=Nurul H. A. |last5=Zraqou |first5=Jamal |last6=Ali |first6=Abdulla M. F. Al |date=2022-12-20 |title=Trojan Horse Infection Detection in Cloud Based Environment Using Machine Learning |url=https://online-journals.org/index.php/i-jim/article/view/35763 |journal=International Journal of Interactive Mobile Technologies |language=en |volume=16 |issue=24 |pages=81–106 |doi=10.3991/ijim.v16i24.35763 |issn=1865-7923|doi-access=free }}</ref>

== Classifications of Trojan horses ==

Trojans are usually classified based on their primary function or intended impact. One major category is the '''banking trojan''', which is designed to steal financial information such as online banking credentials, credit card numbers, or cryptocurrency wallet keys.<ref>{{cite web
|title        = What are Banking Trojans?
|author       = GeeksforGeeks Staff
|date         = July 23, 2025
|website      = GeeksforGeeks
|url          = https://www.geeksforgeeks.org/ethical-hacking/what-are-banking-trojans/
|access-date  = October 5, 2025
}}</ref> Zeus and TrickBot are among the most studied examples of this type. Another category is the '''remote access trojan''', ('''RAT'''), which allows attackers to gain full control over an infected system, enabling them to install additional software, access files, or monitor user activity.<ref>{{cite web
|title        = What is a Remote Access Trojan (RAT)?
|author       = NortonLifeLock Editors
|date         = March 14, 2024
|website      = Norton Blog
|publisher    = NortonLifeLock
|url          = https://us.norton.com/blog/malware/remote-access-trojan
|access-date  = October 5, 2025
}}</ref>

Some trojans are primarily [[Download|downloaders]], meaning they serve as an initial infection stage by installing other forms of malware once inside a system. These often pave the way for [[Ransomware|ransomware]], [[Spyware|spyware]], or [[Botnet|botnet]] recruitment.<ref>{{cite web
|title        = 17 types of Trojans and how to defend against them
|author       = Andy Greenberg
|date         = June 21, 2023
|website      = CSO Online
|publisher    = IDG Communications, Inc.
|url          = https://www.csoonline.com/article/570233/17-types-of-trojans-and-how-to-defend-against-them.html
|access-date  = October 5, 2025
}}</ref> Information-stealing trojans are also common, collecting sensitive data such as browser cookies, stored credentials, or documents without the user’s knowledge. Furthermore, '''fake antivirus trojans''' imitate legitimate security software, tricking users into paying for unnecessary or harmful services.<ref>{{cite web
|title        = What is a Trojan and how does it work?
|author       = NortonLifeLock Editors
|date         = February 5, 2024
|website      = Norton Blog
|publisher    = NortonLifeLock
|url          = https://us.norton.com/blog/malware/what-is-a-trojan
|access-date  = October 5, 2025
}}</ref> Because trojans can be adapted for multiple purposes, many modern types have overlapping features, mixing elements of [[Backdoor (computing)|backdoors]], spyware, and downloaders.<ref>{{cite web
|title        = What is a Trojan and how does it work?
|author       = NortonLifeLock Editors
|date         = February 5, 2024
|website      = Norton Blog
|publisher    = NortonLifeLock
|url          = https://us.norton.com/blog/malware/what-is-a-trojan
|access-date  = October 5, 2025
}}</ref> This adaptability has been a major factor in their prevalence as one of the most common forms of malware.

==Linux ls example==
A trojan horse is a [[Computer program|program]] that purports to perform some legitimate function, yet upon execution it compromises the user's security.<ref name="Wood1985"/> One simple example<ref name="CETS2023"/> 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., <code>/tmp/ls</code>). Then, any victim who tried to run <code>ls</code> from that directory — ''if and only if'' the victim's executable search <code>PATH</code> unwisely<ref name="CETS2023"/> included the current directory <code>.</code> — would execute <code>/tmp/ls</code> instead of <code>/usr/bin/ls</code>, and have their home directory deleted.
<syntaxhighlight lang="sh">
#!/usr/bin/env bash
rm -rf ~ 2>/dev/null # Remove the user's home directory, then remove self.
rm $0
</syntaxhighlight>
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.<ref name="Wood1985"/> 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 attack]]s.

== Prevention and mitigation ==

Preventing trojan infections requires a mix of user awareness, technical safeguards, and proactive security practices. Educating users about the dangers of downloading unverified files or executing unknown programs remains an effective way to prevent attacks.<ref>{{cite web
|title        = Recovering from Viruses, Worms, and Trojan Horses
|author       = Cybersecurity and Infrastructure Security Agency
|date         = March 10, 2024
|website      = CISA.gov
|publisher    = U.S. Department of Homeland Security
|url          = https://www.cisa.gov/news-events/news/recovering-viruses-worms-and-trojan-horses
|access-date  = October 5, 2025
}}</ref> Security software such as antivirus and anti-malware programs can help detect, quarantine, and remove trojans when kept up to date.<ref>{{cite web
|title        = Guide to Malware Incident Prevention and Handling
|author1      = Tim Grance
|author2      = Karen Kent
|date         = November 2008
|publisher    = National Institute of Standards and Technology
|series       = NIST Special Publication 800-83 Revision 1
|url          = https://nvlpubs.nist.gov/nistpubs/specialpublications/nist.sp.800-83r1.pdf
|access-date  = October 5, 2025
}}</ref> Safe browsing practices—such as avoiding suspicious links, refraining from downloading software from untrusted sources, and exercising caution with email attachments—are also key to reducing risk.<ref>{{cite web
|title        = On the Internet: Safety Resources and Scam Prevention
|author       = Federal Bureau of Investigation
|date         = April 2025
|website      = FBI.gov
|url          = https://www.fbi.gov/how-we-can-help-you/scams-and-safety/on-the-internet
|access-date  = October 5, 2025
}}</ref> Additionally, maintaining regular software and operating system updates ensures that known vulnerabilities are patched, making it harder for trojans to exploit weaknesses.<ref>{{cite web
|title        = Recovering from Viruses, Worms, and Trojan Horses
|author       = Cybersecurity and Infrastructure Security Agency
|date         = March 10, 2024
|website      = CISA.gov
|publisher    = U.S. Department of Homeland Security
|url          = https://www.cisa.gov/news-events/news/recovering-viruses-worms-and-trojan-horses
|access-date  = October 5, 2025
}}</ref> In professional environments, network firewalls, intrusion detection systems (IDS), and email filtering tools are commonly used to block suspicious traffic and prevent trojans from communicating with external servers. Regular security checks, employee training programs, and routine data backups further strengthen defenses and help reduce potential damage in the event of an infection.<ref>{{cite web
|title        = AA20-245A: Technical Approaches to Uncovering and Remediating Malicious Activity
|author       = Cybersecurity and Infrastructure Security Agency
|date         = September 1, 2020
|website      = CISA Cybersecurity Advisories
|publisher    = U.S. Department of Homeland Security
|url          = https://www.cisa.gov/news-events/cybersecurity-advisories/aa20-245a
|access-date  = October 5, 2025
}}</ref>

==Modern developments and detection techniques==
Modern trojan horses have changed beyond traditional file-based malware, progressively using techniques designed to avoid signature-based security tools. An example of this approach is fileless malware, in which trojans operate mainly in system memory and rely on legitimate administrative tools like PowerShell or Windows Management Instrumentation (WMI). By lowering or removing malicious files on disk, fileless trojans are more difficult for conventional antivirus software to detect.<ref>{{cite web |title=Fileless Malware |publisher=National Institute of Standards and Technology (NIST) |url=https://www.nist.gov
|access-date=2025-03-06}}</ref>
In recent years, trojans have expanded to mobile and embedded platforms. Android trojans are often distributed through unofficial application stores or phishing campaigns and may request more permissions that allow access to messages, stored credentials, or financial information.<ref>{{cite report |title=ENISA Threat Landscape for Mobile Malware |publisher=European Union Agency for Cybersecurity (ENISA) |url=https://www.enisa.europa.eu
|access-date=2025-03-06}}</ref> Trojans targeting Internet of Things (IoT) devices often take advantage of weak authentication practices or unpatched firmware, which in turn allows compromised devices to be incorporated into large botnets used for distributed denial-of-service (DDoS) attacks.<ref>{{cite web |title=Risks Posed by Internet of Things (IoT) Devices |publisher=Cybersecurity and Infrastructure Security Agency (CISA) |url=https://www.cisa.gov
|access-date=2025-03-06}}</ref>
To counter these developments, modern security systems increasingly rely on behavior-based detection techniques. Rather than depending only on known malware signatures, behavioral analysis monitors system activity for signs such as unauthorized privilege escalation or suspicious network communication patterns.<ref>{{cite web |title=Behavior-Based Malware Detection |publisher=Symantec Security Blog |url=https://symantec-enterprise-blogs.security.com
|access-date=2025-03-06}}</ref> Alongside behavior-based detection, machine learning–based methods have been developed to classify and detect trojans by identifying irregularities within large-scale system and network telemetry data. While these approaches can help detection rates, they also present challenges related to false positives and the clarity of automated decision-making systems<ref>{{cite journal |last1=Buczak |first1=A. L. |last2=Guven |first2=E. |title=A Survey of Data Mining and Machine Learning Methods for Cyber Security Intrusion Detection |journal=IEEE Communications Surveys & Tutorials |year=2016}}</ref>
==Notable examples==
There have been many well-known trojans that have played an important role in the history of cybersecurity. An early example is the [[AIDS (Trojan horse)|AIDS trojan]], developed in 1989. It is considered one of the first forms of ransomware, as it encrypted filenames on infected computers and demanded payment to restore them.<ref>{{cite web
|title        = The History of Ransomware: The AIDS Trojan Attack
|author       = Ransomware.org Staff
|date         = May 17, 2024
|website      = Ransomware.org
|url          = https://ransomware.org/what-is-ransomware/the-history-of-ransomware/#aids-trojan-attack
|access-date  = October 5, 2025
}}</ref>
[[File:You_Are_An_Idiot_screen.gif|thumb|Full animation of the "You Are An Idiot" Trojan horse]]
A famous example is the '''You Are An Idiot''' '''trojan''', developed in 2002. It originated from a comedy sketch by American radio personality [[Rick Dees]] on his 1984 album ''Put It Where the Moon Don’t Shine''. Specifically, the vocal jingle was featured during a prank call segment titled "Candid Phone: Dog Funeral." The audio later gained notoriety in the early 2000s when it was sampled for the YouAreAnIdiot.org website, which functioned as a browser-based trojan. This site overwhelmed users by displaying flashing black-and-white smiley faces while continuously looping the vocal track. It became a legendary "pop-up bomb" because it would spawn six new windows every time a user attempted to close one and disabled standard hotkeys like Alt+F4. While it did not cause permanent damage to files, it frequently exhausted system resources and caused computers to freeze. Safe versions of the website were later created without the spawn feature.<ref name=":1">{{Cite web |last=Powell|first=Olivia|date=2023-02-21|title=The ultimate guide to malware|url=https://www.cshub.com/malware/articles/the-ultimate-guide-to-malware|access-date=2026-03-08|website=Cyber Security Hub|language=en}}</ref>

Another famous example is the [[Zeus (malware)|Zeus trojan]], first identified in 2007. Zeus mainly targeted Microsoft Windows systems and was designed to steal banking credentials through [[man-in-the-browser]] attacks, which infected a user's browser to intercept and manipulate data, leading to widespread financial losses and data breaches.<ref>{{cite web
|title        = What is Zeus Malware?
|author       = CrowdStrike Intelligence Team
|date         = August 8, 2024
|website      = CrowdStrike
|url          = https://www.crowdstrike.com/en-us/cybersecurity-101/malware/zeus-malware/
|access-date  = October 5, 2025
}}</ref> In 2015, in Ukraine, an attacker group, by means of an authenticated computer that was controlled remotely using a [[remote access trojan]], gained access to a controller server, that resulted in an electricity outage for 80.000 people. <ref>{{Cite news |last=Zetter |first=Kim |title=Everything We Know About Ukraine's Power Plant Hack |url=https://www.wired.com/2016/01/everything-we-know-about-ukraines-power-plant-hack/ |access-date=2026-04-10 |work=Wired |language=en-US |issn=1059-1028}}</ref><ref>{{Cite web |date=2023-02-03 |title=¿Qué es un troyano de acceso remoto (RAT)? Cómo detectarlos y mucho más {{!}} Proofpoint ES |url=https://www.proofpoint.com/es/threat-reference/remote-access-trojan |access-date=2026-04-10 |website=Proofpoint |language=es}}</ref> In 2016, the [[MEMZ|MEMZ trojan]], a Windows-based program, became widely recognized for its complex and destructive payloads. MEMZ gained notoriety for displaying unusual visual effects on infected machines and ultimately rendering the systems unusable.[[File:Map of Operation Trojan Shield.jpg|thumb|Map of countries touched by ANOM]]

===Private and governmental===
* [[ANOM]] – FBI
* [[Chaos Computer Club#Staatstrojaner affair|0zapftis / r2d2 StaatsTrojaner]] – DigiTask
* [[FinFisher]] – Lench IT solutions / Gamma International 
* [[Hacking Team#Products and capabilities|DaVinci / Galileo RCS]] – HackingTeam
* [[Magic Lantern (spyware)|Magic Lantern]] – FBI
* [[2020 United States federal government data breach|SUNBURST]] – [[Foreign Intelligence Service (Russia)|SVR]]/[[Cozy Bear]] (suspected)
* [[Tailored Access Operations#QUANTUM attacks|TAO QUANTUM/FOXACID]] – NSA
* [[WARRIOR PRIDE]] – GCHQ

===Publicly available===
* [[EGABTR]] – late 1980s
* [[Netbus]] – 1998 (published)<ref name="Kulakow2001"/>
* [[Sub7]] by Mobman – 1999 (published)
* [[Back Orifice]] – 1998 (published)
* [[Y3K]] by Tselentis brothers – 2000 (published)
* [[Beast (Trojan horse)|Beast]] – 2002 (published)
* YouAreAnIdiot by Andrew Regner - 2002 (published)
* [[Bifrost (Trojan horse)|Bifrost Trojan]] – 2004 (published)
* [[DarkComet]] – 2008-2012 (published)
* [[Blackhole exploit kit]] – 2012 (published)
* [[Gh0st RAT]] – 2009 (published)
* [[MiniPanzer and MegaPanzer|MegaPanzer BundesTrojaner]] – 2009 (published)<ref name="MegaPanzer2016"/><ref name="MiniPanzer2016"/>
* [[MEMZ]] by Leurak – 2016 (published)
===Detected by security researchers===
* [[Twelve Tricks]] – 1990
* [[Clickbot.A]] – 2006 (discovered)
* [[Zeus (Trojan horse)|Zeus]] – 2007 (discovered)
* [[Trojan BackDoor.Flashback|Flashback Trojan]] – 2011 (discovered)
* [[ZeroAccess botnet|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)<ref name="Lookout2015"/><ref name="Neal2015"/><ref name="Bentley2015"/><ref>{{cite web
  |url=https://betanews.com/2015/11/05/shuanet-shiftybug-and-shedun-malware-could-auto-root-your-android/
  |title=Shuanet, ShiftyBug and Shedun malware could auto-root your Android
  |date=November 5, 2015}}</ref><ref>{{cite web |url=http://www.techtimes.com/articles/104373/20151109/new-family-of-android-malware-virtually-impossible-to-remove-say-hello-to-shedun-shuanet-and-shiftybug.htm
  |title=New Family of Android Malware Virtually Impossible To Remove: Say Hello To Shedun, Shuanet And ShiftyBug
  |first=Tech
  |last=Times
  |date=November 9, 2015}}</ref><ref>{{cite web | last=Goodin | first=Dan | title=Android adware can install itself even when users explicitly reject it | website=Ars Technica | date=2015-11-19 | url=https://arstechnica.com/information-technology/2015/11/android-adware-can-install-itself-even-when-users-explicitly-reject-it/ | access-date=2025-08-08}}</ref>

==See also==
{{colbegin}}
* {{annotated link|Computer security}}
* {{annotated link|Cuckoo's egg (metaphor)}}
* {{annotated link|Cyber spying}}
* {{annotated link|Dancing pigs}}
* {{annotated link|Exploit (computer security)}}
* {{annotated link|Industrial espionage}}
* {{annotated link|Hardware Trojan}}
* {{annotated link|Phishing}}
* {{annotated link|Principle of least privilege}}
* {{annotated link|Privacy-invasive software}}
* {{annotated link|Remote administration}}
* {{annotated link|Remote administration software}}
* {{annotated link|Reverse connection}}
* {{annotated link|Rogue security software}}
* {{annotated link|Scammers}}
* {{annotated link|Technical support scam}}
* {{annotated link|Timeline of computer viruses and worms}}
* {{annotated link|Zombie (computer science)}}

{{colend}}

==References==
<references>
<ref name="Bentley2015">{{cite web |author=Michael Bentley |title=Lookout discovers new trojanized adware; 20K popular apps caught in the crossfire |website=blog.lookout.com |url=https://blog.lookout.com/blog/2015/11/04/trojanized-adware/ |access-date=2016-04-08 |url-status=dead |archive-url=https://web.archive.org/web/20170219042903/https://blog.lookout.com/blog/2015/11/04/trojanized-adware/ |archive-date=2017-02-19}}</ref>

<ref name="Bitdefender2009">{{cite web |title=BitDefender Malware and Spam Survey finds E-Threats Adapting to Online Behavioral Trends |date=2009-08-03 |website=[[Bitdefender|BitDefender]] |url=http://news.bitdefender.com/NW1094-en--BitDefender-Malware-and-Spam-Survey-finds-E-Threats-Adapting-to-Online-Behavioral-Trends.html |access-date=2020-03-27 |url-status=dead |archive-url=https://web.archive.org/web/20090808080907/http://news.bitdefender.com/NW1094-en--BitDefender-Malware-and-Spam-Survey-finds-E-Threats-Adapting-to-Online-Behavioral-Trends.html |archive-date=2009-08-08}}</ref>

<ref name="Broadcom2013">{{cite web |title=Difference between viruses, worms, and trojans |url=https://knowledge.broadcom.com/external/article?legacyId=tech98539 |website=Symantec Security Center |publisher=Broadcom Inc. |access-date=2020-03-29 |archive-url=https://archive.today/20130819122702/http://www.symantec.com/business/support/index?page=content&id=TECH98539#selection-3435.1-3585.1 |archive-date=2013-08-19 |url-status=live}}{{cbignore|bot=InternetArchiveBot}}</ref>

<ref name="CETS2023">{{cite web |url=https://cets.seas.upenn.edu/answers/dot-path.html |title=What's wrong with having '.' in your $PATH? |website=CETS Answers |publisher=University of Pennsylvania Computing and Educational Technology Services |access-date=2023-11-28}}</ref>

<ref name="Collins2020">{{cite web |title=trojan |url=https://www.collinsdictionary.com/dictionary/english/trojan |website=Collins COBUILD Advanced Learner’s Dictionary |access-date=2020-03-29}}</ref>

<ref name="Crapanzano2003">{{cite report |author=Jamie Crapanzano |title=Deconstructing SubSeven, the Trojan Horse of Choice |date=2003 |url=http://www.sans.org/reading_room/whitepapers/malicious/deconstructing_subseven_the_trojan_horse_of_choice_953 |publisher=[[SANS Institute]] |access-date=2021-05-10}}</ref>

<ref name="Datta2014">{{cite web |author=Ganesh Datta |title=What are Trojans? |url=http://securaid.com/windows/2014/08/what-are-trojans/ |work=SecurAid |archive-url=https://archive.today/20140812015643/http://securaid.com/windows/2014/08/what-are-trojans/ |archive-date=2014-08-12 |url-status=dead |date=2014-08-07 |access-date=2020-03-27}}</ref>

<ref name="Gregg2015">{{cite book |author=Michael Gregg |title=The Network Security Test Lab: A Step-by-Step Guide |entry=Backdoors and Trojans |publisher=Wiley |year=2015 |pages=338–340 |isbn=978-1-118-98705-6 |url=https://archive.org/details/networksecurityt0000greg/page/338 |access-date=2020-03-29 |quote=Unlike a virus or worm, Trojans cannot spread themselves.}}</ref>

<ref name="Karger1974">{{cite journal |author1=Paul A. Karger |author2=Roger R. Schell |title=Multics Security Evaluation: Vulnerability Analysis, ESD-TR-74-193 |journal=HQ Electronic Systems Division: Hanscom AFB, MA |volume=2 |date=June 1974 |url=http://csrc.nist.gov/publications/history/karg74.pdf |access-date=2017-12-24 |archive-url=https://web.archive.org/web/20110709024412/http://csrc.nist.gov/publications/history/karg74.pdf |archive-date=2011-07-09 |url-status=dead |at=4.2.1 |quote=...some sort of protection from user written applications programs that may contain "Trojan Horses" {{sic}}}}</ref>

<ref name="Karger2002">{{cite journal |author1=Paul A. Karger |author2=Roger R. Schell |title=Thirty Years Later: Lessons from the Multics Security Evaluation |journal=ACSAC |date=2002 |pages=119–126 |url=https://www.acsac.org/2002/papers/classic-multics.pdf}}</ref>

<ref name="Kulakow2001">{{cite report |author=Seth Kulakow |title=NetBus 2.1: Is It Still a Trojan Horse or an Actual Valid Remote Control Administration Tool? |url=https://www.giac.org/paper/gsec/1185/netbus-21-trojan-horse-actual-valid-remote-control-administration-tool/102342 |publisher=[[SANS Institute]] |date=2001 |access-date=2025-10-03 |url-status=live |archive-url=https://web.archive.org/web/20220511154807/https://www.giac.org/paper/gsec/1185/netbus-21-trojan-horse-actual-valid-remote-control-administration-tool/102342 |archive-date=2022-05-11}}</ref>

<ref name="Lookout2015">{{cite web |title=Trojanized Adware Family Abuses Accessibility Service |website=Lookout.com |date=2015-11-19 |url=https://blog.lookout.com/blog/2015/11/19/shedun-trojanized-adware/}}</ref>

<ref name="MegaPanzer2016">{{cite web |author=orbitalsatelite |title=Mega-Panzer |website=SourceForge |date=2016-09-21 |url=https://sourceforge.net/projects/mega-panzer/}}</ref>

<ref name="Microsoft2020">{{cite encyclopedia |entry=trojan horse |title=Microsoft Style Guide |publisher=[[Microsoft]] |url=https://docs.microsoft.com/en-us/style-guide/a-z-word-list-term-collections/t/trojan-horse-trojan |access-date=2020-03-29}}</ref>

<ref name="MiniPanzer2016">{{cite web |author=orbitalsatelite |title=Mini-Panzer |website=SourceForge |date=2016-09-18 |url=https://sourceforge.net/projects/mini-panzer/}}</ref>

<ref name="Neal2015">{{cite web |author=[[Dave Neal]] |title=Shedun trojan adware is hitting the Android Accessibility Service |date=2015-11-20 |url=http://www.theinquirer.net/inquirer/news/2435721/shedun-trojan-adware-is-hitting-the-android-accessibility-service |website=[[The Inquirer]] |publisher=Incisive Business Media |access-date=2020-03-27 |archive-url=https://web.archive.org/web/20151122002729/http://www.theinquirer.net/inquirer/news/2435721/shedun-trojan-adware-is-hitting-the-android-accessibility-service |archive-date=2015-11-22 |url-status=unfit}}</ref>

<ref name="Thompson1984">{{cite journal |title=Reflection on Trusting Trust |author=[[Ken Thompson]] |journal=[[Communications of the ACM]] |volume=27 |number=8 |pages=761–763 |date=1984 |url=https://dl.acm.org/ft_gateway.cfm?id=1283940&type=pdf |doi=10.1145/358198.358210 |doi-access=free|url-access=subscription }}</ref>

<ref name="Wood1985">{{cite book |author1=Patrick H. Wood |author2=Stephen G. Kochan |title=UNIX System Security |publisher=Hayden Books |year=1985 |pages=42–43 |isbn=0-8104-6267-2}}</ref>
</references>

==Notes==
{{Notelist}}

==External links==
*{{Commonscatinline|Trojan horse (malware)}}
*{{cite web
  |title=CERT Advisory CA-1999-02 Trojan Horses
  |url=https://resources.sei.cmu.edu/asset_files/WhitePaper/1999_019_001_496184.pdf#page=14 
  |website=Carnegie Mellon University Software Engineering Institute
  |archive-url=https://web.archive.org/web/20001017172300/http://www.cert.org/advisories/CA-1999-02.html
  |archive-date=2000-10-17
  |access-date=15 September 2019
  |url-status=live}}

{{Malware}}
{{Information security}}{{Software distribution}}{{Authority control}}

{{DEFAULTSORT:Trojan Horse (Computing)}}
[[Category:Trojan horses| ]]
[[Category:Social engineering (security)]]
[[Category:Spyware]]
[[Category:Cyberwarfare]]
[[Category:Security breaches]]