If you find a virus keeps coming back after you delete it, it’s most probably infected the System Restore folder, the best way to solve this is to disable System Restore, reboot your machine and then enable it again. After all, run a full avast! scanning. System Restore cannot be disabled on Windows 9x and it’s not available in Windows 2k.
Windows attempts to protect files that are deleted from the system folders (just in case it was an accident), so they can be restored if required.
The problem is many malware writers are wise to that and put their files in the system folders, this is also done to confuse you into thinking you could be deleting an important system file.
Disable system restore, reboot, scan and if clean enable system restore again.