Trojan horse (computing)
|This article needs additional citations for verification. (November 2013)|
A Trojan horse, or Trojan, in computing is a non-self-replicating type of malware program containing malicious code that, when executed, carries out actions determined by the nature of the Trojan, typically causing loss or theft of data, and possible system harm. The term is derived from the story of the wooden horse used to trick defenders of Troy into taking concealed warriors into their city in ancient Greece, because computer Trojans often employ a form of social engineering, presenting themselves as routine, useful, or interesting in order to persuade victims to install them on their computers.
A Trojan often acts as a backdoor, contacting a controller which can then have unauthorized access to the affected computer. The Trojan and backdoors are not themselves easily detectable, but if they carry out significant computing or communications activity may cause the computer to run noticeably slowly. Malicious programs are classified as Trojans if they do not attempt to inject themselves into other files (computer virus) or otherwise propagate themselves (worm). A computer may host a Trojan via a malicious program a user is duped into executing (often an e-mail attachment disguised to be unsuspicious, e.g., a routine form to be filled in) or by drive-by download.
Purpose and uses
A Trojan may give a hacker remote access to a targeted computer system. Operations that could be performed by a hacker, or be caused unintentionally by program operation, on a targeted computer system include:
- Use of the machine as part of a botnet (e.g. to perform automated spamming or to distribute Denial-of-service attacks)
- Electronic money theft
- Data theft, including confidential files, sometimes for industrial espionage, and information with financial implications such as passwords and payment card information
- Modification or deletion of files
- Downloading or uploading of files for various purposes
- Downloading and installing software, including third-party malware and ransomware
- Keystroke logging
- Watching the user's screen
- Viewing the user's webcam
- Controlling the computer system remotely
- Encrypting files; a ransom payment may be demanded for decryption, as with the CryptoLocker ransomware
- Modifications of registry
- Using computer resources for Bitcoin mining.
- Linking computer to Botnet
- Using infected computer as proxy for illegal activities and attacks on other computers.
More likely to be unintended or merely malicious, rather than criminal, consequences:
- Crashing the computer, e.g. with "blue screen of death" (BSOD)
- Data corruption
- Formatting disks, destroying all contents
Trojan horses in this way may require interaction with a malicious controller (not necessarily responsible for distributing the Trojan horse) to fulfill their purpose. It is possible for those involved with Trojans to scan computers on a network to locate any with a Trojan horse installed, which the hacker can then control.
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, 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 horse 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 horse.
Due to the popularity of botnets among hackers and the availability of advertising services that permit authors to violate their users' privacy, Trojan horses 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-percent of the global malware detected in the world." Trojans have a relationship with worms, as they spreads with the help given by worms and travel across the internet with them.
Antivirus company BitDefender says that approximately 15% of computers are members of a botnet, usually recruited by a Trojan infection.
Common Trojan horses
- PC Optimizer Pro (unknown creator)
- Netbus (by Carl-Fredrik Neikter)
- Subseven or Sub7(by Mobman)
- Back Orifice (Sir Dystic)
- The Blackhole exploit kit
- Flashback Trojan (Trojan BackDoor.Flashback)
- Computer security
- Remote administration (Remote Access Tool trojans)
- Cyber spying
- Dancing pigs
- Exploit (computer security)
- Industrial espionage
- Principle of least privilege
- Privacy-invasive software
- Reverse connection
- Rogue security software
- Social engineering (security)
- Timeline of computer viruses and worms
- Landwehr, C. E; A. R Bull, J. P McDermott, W. S Choi (1993). "A taxonomy of computer program security flaws, with examples". DTIC Document. Retrieved 2012-04-05.
- "Trojan Horse Definition". Retrieved 2012-04-05.
- "Trojan horse". Webopedia. Retrieved 2012-04-05.
- "What is Trojan horse? - Definition from Whatis.com". Retrieved 2012-04-05.
- "Trojan Horse: [coined By MIT-hacker-turned-NSA-spook Dan Edwards] N.". Retrieved 2012-04-05.
- "What is the difference between viruses, worms, and Trojans?". Symantec Corporation. Retrieved 2009-01-10.
- "VIRUS-L/comp.virus Frequently Asked Questions (FAQ) v2.00 (Question B3: What is a Trojan Horse?)". 9 October 1995. Retrieved 2012-09-13.
- Jamie Crapanzano (2003): "Deconstructing SubSeven, the Trojan Horse of Choice", SANS Institute, Retrieved on 2009-06-11
- Vincentas (11 July 2013). "Trojan Horse in SpyWareLoop.com". Spyware Loop. Retrieved 28 July 2013.
- BitDefender.com Malware and Spam Survey
- Datta, Ganesh. "What are Trojans?". SecurAid.
- Burt, Jeffrey (2012-04-19). "HP: Fewer but More Dangerous Software Security Vulnerabilities". eWeek.com. Ziff Davis. Retrieved 2012-04-20. "[...] Web exploit kits continued to be popular in 2011. HP pointed to the Blackhole Exploit Kit, which officials said is used by most hackers and hit an infection rate of more than 80 percent in late November 2011."
- Carnegie Mellon University (1999): "CERT Advisory CA-1999-02 Trojan Horses", Retrieved on 2009-06-10.