Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
An Iranian trojan. Gives full control to the attacker over the victims machine: log keystrokes, take screenshots, record audio, and mess with various files and system settings.
The "server" program can be customised by the attacker, and is usually compressed with UPX.