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 drive-by download. 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.
Unlike computer viruses and worms, Trojans generally do not attempt to inject themselves into other files or otherwise propagate themselves
1. Destructive Activity
Crashing the computer or device.
Modification or deletion of files.
Formatting disks, destroying all contents.
Spread malware across the network.
Spy on user activities and access sensitive information