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In computing, a Trojan horse (or simply Trojan) is any malware that misleads users of its true intent by disguising itself as a standard program. The term is derived from the ancient Greek story of the deceptive Trojan Horse that led to the fall of the city of Troy.[1]
Trojans are generally spread by some form of social engineering. For example, where a user is duped into executing an email attachment disguised to appear innocuous (e.g., a routine form to be filled in), or by clicking on a fake advertisement on social media or anywhere else. 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 computer.[2] 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.[3]
Greek soldiers, unable to penetrate the defenses of the city of Troy during a years-long war, presented the city with a peace offering of a large wooden horse.