Trojan
Malware disguised as legitimate software that delivers a hidden payload when run.
A trojan masquerades as legitimate software and runs a hidden malicious payload when the user is tricked into executing it. The defining trait — and a favorite exam point — is that trojans do not self-replicate, which separates them from viruses (need a host file) and worms (spread themselves over networks). Remote Access Trojans (RATs) are a potent variety, giving the attacker persistent, interactive control of the victim’s machine.