So you have a trojan 
Try a full scan with avast, a scan at boot time and, if you can, I suggest an on-line scanning by Trend Micro (www.trendmicro.com).
Maybe you can send an IM to whocares and ask for help.
See the virus board and read his advices: http://forum.avast.com/index.php?board=4;action=display;threadid=5373