Trojans are deceptive programs that appear to perform one function, but in fact perform another, malicious function. They might be disguised as free software, videos or music, or seemingly legitimate advertisements.

The term “trojan virus” is not technically accurate; according to most definitions, trojans are not viruses. A virus is a program that spreads by attaching itself to other software, while a trojan spreads by pretending to be useful software or content. Many experts consider spyware programs, which track user activity and send logs or data back to the attacker, as a type of trojan.