A fake virus warning is doing the email rounds asking people to delete a harmless executable Windows file and to pass on the warning to others.

The perverse but amusing hoax tells users to delete the sulfnbk.exe file, a utility used to restore long file names. The message warns people that it's a virus undetectable by antivirus software. Diligent users who search for the file and find it may presume the warning was accurate and delete it.

Standard antivirus screens will not detect the warning email, because it is not a virus. But if users comply with the message, by deleting the file and forwarding the email to others, they will have serious problems with long filename recovery.

The message begins, 'Follow the instructions, I had it!!!!!...', according to Avert Labs, the division of antivirus firm McAfee that tracks viruses and sends out alerts. The body of the mail reads something like: 'I received this message from a friend and today it is true. I searched for the file following the next instruction and I found it, I had it without knowing'. It then lists instructions for finding and deleting the file.

The virus hoaxers appear to be playing on concerns about the sulfnbk.exe file which was previously infected by the Magistr worm. The current hoax is unrelated to the earlier worm, which can be detected and destroyed using updated antivirus software.

Instructions for restoring the deleted file may be found here.