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.
Tofsee is a trojan targeted to the gaming community in China. Once infected, it will monitor the victim's network for specific hosts looking to login to gaming sites. It then stores the stolen information in a .ini file to be sent to the attacker at their convenience. It also disables several useful security applications by applying the appropriate Image File Executions Options.