Trojan horse (computing)

In computing, Trojan horse, or Trojan, is any malicious computer program which is used to hack into a computer by misleading users of its true intent. The term is derived from the Ancient Greek story of the wooden horse that was used to help Greek troops invade the city of Troy by stealth.

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 be unsuspicious, (e.g., a routine form to be filled in), or by drive-by download. 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. This infection allows an attacker to access users' personal information such as banking information, passwords, or personal identity (IP address).

Unlike computer viruses and worms, Trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves.

If installed or run with elevated privileges a Trojan will generally have unlimited access. What it does with this power depends on the motives of the attacker.

Trojan horses in this way may require interaction with a malicious controller (not necessarily 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.

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