A Trojan horse, or Trojan, is a standalone malicious file or program that does not attempt to inject itself into other files unlike a computer virus and often masquerades as a legitimate file or program. Trojan horses can make copies of themselves, steal information, or harm their host computer systems. The first and many current Trojan horses attempt to appear as helpful programs. Others rely on drive-by downloads in order to reach target computers. The term is derived from the Trojan Horse story in Greek mythology because Trojan horses employ a form of social engineering,presenting themselves as harmless, useful gifts, in order to persuade victims to install them on their computers (just as the Trojans were tricked into taking the Trojan Horse inside their gates). A Trojan may give a hacker remote access to a targeted computer system.
Contributions by RainR, Matey, and 18.104.22.168.