Trojan Horse Backdoor Generic 12 AAVT – AVG cannot remove it.
http://forums.whatthetech.com/Trojan_Horse_BackDoor_Generic_12_AAVT_t109934.html
download of combofix http://download.bleepingcomputer.com/sUBs/ComboFix.exe
I would recommend backing up the system before running the ComboFix program.
The other option is to try this from AVG
http://forums.avg.com/ww-en/avg-free-forum?sec=thread&act=show&id=63271