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.
From the Website:
Remote HAVOC is simply the best prank program available on the Internet today! With the help of this program, you will be able to connect to any other networked computer and just go nuts! You'll get an arsenal of about 20 commands, all of which are COMPLETELY controlled by you, and can be executed at any time!