Anti-virus companies are warning against a hoax message which warns users that a file on their Windows machine needs deleting. The so-called virus it details does not exist.

An email headed "RED ALERT-WARNING!! THIS VIRUS IS NOT DETECTABLE!!!" is being forwarded around the world with instructions on deleting the sulfnbk executable.

It claims that on 1 June, a virus embedded in the file will erase files on the hard drive. Many Windows 95 and 98 machines will have a legitimate copy of this file, as it is used to restore long filenames.

Andre Post, researcher at Symantec, said the hoax was taking "social engineering to the extreme. It is using the human as the payload trigger and the distribution method."

He added that as home users and corporations become more aware of the potential threats that malicious viruses pose, "many people may be inclined to follow the advice of virus alerts such as this one".

Post warned that although the message contains no malicious code itself, the fact that it asks a user to delete files makes it as "damaging as a real virus".

Users who have deleted the sulfnbk executable are urged to check the website of their anti-virus provider for advice.