As the world tightens up its defences to ward off another deadly computer virus, hoax virus warnings are running wild and causing their own disruption.

The Life Stages worm, and the Love Bug before it, have caused untold problems for computer users. But hoax writers seem to be preying on user paranoia with increasingly ridiculous warnings.

One hoax circulating via email this week warns of a mobile phone virus. The alert tells users not to answer any phone calls which show the word 'UNAVAILABLE!'on a mobile phone display. It says answering the call will infect the phone with a virus.

Antivirus company Sophos, which is also named on the email, confirmed that the warning is a hoax, and urged users to ignore it and not forward it to friends and colleagues. Graham Cluley, senior technology consultant at the company, said continued re-forwarding of hoaxes like this wastes time and email bandwidth.

"Virus hoaxes are actually more of a problem than real viruses. With real ones, you can do something about it by installing antivirus software. With these hoax emails, people talk about them down the pub, they are discussed on the radio and they can even have a similar type of payload to the Love Bug," said Cluley.

"There are no such things as mobile phone viruses yet," he added, saying that virus hoaxes play on users' fears of virus infection, particularly following widespread and destructive infections from recent examples such as the Love Bug.

Previous hoax viruses include Good Times, Elf Bowling, the Nokia Giveaway chain letter and WIn a Holiday.