Anti-virus developers are warning that they cannot develop an antidote until the virus appears. Far from destroying vital files, the virus will make sure everyone can see them.

The new virus is expected to be a variant of either Melissa or the Explore.Zip worm, both of which have cost businesses millions in recent weeks.

Both Melissa and the Explore.Zip worm rely on people opening email attachments. Once into the computer the virus sends a message to everyone in the victim's in-box and then destroys every file written in Microsoft Word, Excel or Powerpoint, among others.

New virus on the block

One variant has already appeared. PrettyPark replicates itself by sending copies to everyone in the victim's address book.

It waits silently until the victim is on the Internet, then sends lists of the victim's user names, password files and address lists to Internet Relay Chat channels. Anti-virus developers are expecting the next step to be a virus which roots around in your files and then posts your documents across the Internet.

"The virus wouldn't be able to tell which of your documents are secret. It might just post your shopping list, or it could be a highly sensitive company document.

"What's more, it would appear as if you sent it," says Graham Cluley of Sophos Anti-Virus.

Several anti-virus makers already have an answer to PrettyPark. But they cannot build a defence against future variants until they encounter them.

Java and ActiveX - next infection target

It is predicted that the next generation of viral infections will hit small Webpage programmes called applets, written in Java and particularly ActiveX.

A recent survey revealed that more than half of medium-sized organisations using an intranet had no security policy in place to respond to the threat of attacks on Java applets.