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.
Comment:
Pero.CN is an exploit run in javascript. Once the victim goes to a site with the extension com.php, exploit Javascript code is executed that redirects and downloads an infected executable file onto the victim's machine.