Trojan horse, or Trojan, is any malicious computer program which misleads users of its true intent. The term is derived from the Ancient Greek story of the deceptive wooden horse that led to the fall of the city of Troy.
Trojans are generally spread by some form of social engineering, for example where a user is duped into executing an e-mail attachment disguised to be unsuspicious, (e.g., a routine form to be filled in), or by clicking on some fake advertisement on social media or anywhere else . Although their payload can be anything, many modern forms act as a backdoor, contacting a controller which can then have unauthorized access to the affected computer.
Trojans may allow an attacker to access users’ personal information such as banking information, passwords, or personal identity. It can infect other devices connected to the network. 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.