Users are being warned not to open junk e-mail messages claiming Osama Bin Laden has been captured.

The messages claim to contain pictures of the al-Qaeda leader's arrest but anyone opening the attachment will fall victim to a Microsoft Windows virus.

Since 1 June anti-virus companies have been catching the junk mail messages in large numbers.

Security firms fear that interest in Bin Laden's whereabouts could spark a big outbreak.

US focus

Several versions of the message have been caught by anti-virus and mail-filtering firms but all bear the same fake information about Bin Laden's arrest.

All versions claim that TV news channels such as CNN and the BBC will soon be reporting the arrest and showing more pictures.

One version of the malicious message claims to contain pictures grabbed from a military TV channel. Another directs people to a website holding videos of the capture.

Anyone opening the attachments or visiting the website will get a version of the Psyme trojan installed on their PC.

James Kay, chief technology officer at Blackspider, said that the company had stopped more than a million copies of the message since it first appeared.

"We've seen a lot of it overnight when the US was awake," said Mr Kay.

"We kind of expected that it would be targeted at the US because of the language used in it," he said.

Warnings about the fake Bin Laden arrest virus have also been issued by Panda Software and F-Secure.

The vulnerability exploited by Psyme is found in Windows 2000, 95, 98, ME, NT, XP and Windows Server 2003. Users were urged to update their version of Windows to close the loophole.

This latest virus is the third to use the name of the al-Qaeda leader to trick people into opening it.

In July last year an e-mail began circulating that claimed to link to a website holding a video of Bin Laden's suicide. Another virus circulating in November 2004 posed as a video message from the al-Qaeda leader.