These are some free virus scanners:
avast! - (this use to be my favorite)
Comodo AntiVirus - (Free for Home and Business users).
ClamWin - Free and open source!
This bit of info was relevant back in September 2004, but should no longer be the case:
Using Windows XP SP2? Notice that some older programs wont work? (Stuff in DOS like EDIT.COM for example).
You may have an incorrect registry setting!
While looking for help, I found this thread on the avast! web site:
That thread lead to this thread, which had a fix:
I have a copy of the fix here:
Basically, the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers doesn't point
to the correct file, preventing things from running (it's supposed to point to the "aswMonVd.dll" file in your avast! folder).
More avast! Info:
Using Task Manager, you can identify the parts of avast! running on your system:
ashserv.exe is part of the on-access scanner.
ashmaisv.exe is the mail scanner.
ashdisp.exe shows the blue ball.
ashcmd.exe is the command line scanner (Pro version)
aswupdsv.exe is the part that checks for updates.
ashQuick.exe is Avast's quick scanner.