A malicious program disguised as legitimate software
A Trojan is a malicious program that is disguised as legitimate software. The term comes from the classical myth of the Trojan horse. During their war against the Trojans, the Greeks left a large wooden horse containing Greek soldiers outside the city of Troy. The Trojans thought it was a gift and brought the horse inside the city walls. As soon as night fell, the Greek soldiers emerged from the horse and opened the city gates, allowing the Greek army to pillage the city. Trojan programs work in a similar way: they look useful or interesting to an unsuspecting user, but are actually harmful when executed.
An attacker can either attach a Trojan to useful software, or he can trick you into thinking the Trojan itself is useful software. Trojans cannot replicate themselves, unlike other types of malware such as viruses or worms.
View the list of Local Resources that can assist Internet users in South Africa.