It's spreading with tremendous speed and thousands of users in Britain have already been sent it.

Alex Shipp Anti-virus expert

Experts said the virus, called Goner, was spreading fast. They warned computer users to immediately delete it.

It was first detected on Tuesday morning in the US but experts believe it was created in Europe.

The US, the UK and France are the worst hit of the 17 countries affected so far. Goner can even disable anti-virus software in a computer.

Deleted files

The rogue e-mail is simply named 'hi' and arrives with an attachment - apparently a screensaver - called "Gone.scr".

The message reads: "How are you? When I saw this screensaver I immediately thought of you. I'm in a harry (sic). I promise you'll love it."

When the attachment is clicked, the malicious software inside it displays a small dialog box, which suggests that a legitimate program is at work.

However, in the background, the virus is busily plundering the address book of any Microsoft Outlook e-mail program it finds. It then sends itself to the addresses in the book, tries to close programs that are running and deletes certain system files.

Armed and dangerous

Alex Shipp, of anti-virus service MessageLabs, said: "It's spreading with tremendous speed and thousands of users in Britain have already been sent it.

"The virus mass-mails itself out through e-mail and attempts to destroy anti-virus software on computers, which could prove extremely problematic for those unfortunate enough to receive it."

He said Goner was nearly as widespread as last year's notorious Love Bug virus, which infected hundreds of thousands of businesses and personal computers across the world, including the US Government.

But it is also more sophisticated in that it can disable anti-virus software. Mr Shipp added: "I think this will be nastier than Love Bug. It has the same spread rate but the clean-up will be a lot harder."

Networks susceptible

It was first discovered at 10.30 GMT and took off five hours later. Mr Shipp said it took advantage of the fad for new screensavers to entice people to double-click on it.

He forecast that it would continue to wreak havoc on Wednesday and would then quieten down as people downloaded the necessary anti-virus software to beat it.

People are warned not to open unfamiliar attachments

Goner only affects users of Microsoft Outlook and Outlook Express.

But Ian Hameroff, business manager of security solutions at Computer Associates International Inc, said people using instant messaging and internet relay chat software were also susceptible to the worm because files could be transferred across those networks.

Computer experts advise people not to open unexpected e-mail attachments, even if the sender is someone familiar.

Computer users are advised to update their anti-virus software at least weekly. At its peak, Love Bug infected 1 in 28 e-mails.

Goner's infection rate reached 1 in 36 and was increasing on Tuesday.