Trojan horse is program that tries to fool user by appearing to be a useful program while actually doing damage to the computer. Unlike Virus, Trojan does not replicate itself. It can perform destructive activities such as allowing backdoor entries to other malwares, monitoring and sending activities to third parties, infecting files, and even allowing complete remote access to someone else.
Trojan can get installed by running a program with intent to installing Trojan on computer. So, be cautious while downloading file, installing unknown software and opening email attachments.
