Sounds like a generic root kit. try this by mcaffee
http://download.cnet.com/McAfee-Rootkit-Detective/3000-8022_4-10720121.html
Of course be careful. Download.com has this warning on the page.
"McAfee Rootkit Detective 1.0 is a program designed and developed by McAfee Avert Labs to proactively detect and clean rootkits that are running on the system.
McAfee Rootkit Detective should only be used by knowledgeable individuals at the direction of, and with the support of, a representative from McAfee Avert Labs or McAfee Technical Support. Improper usage of this tool could result in damage to your applications or operating system."
You can also uninstall Avast and use Avg.
Housecall.antivirus.com also has a free online antivirus scan.
Symantec also has a free online security and virus scan. Not sure if they also remove viruses with this one
