BUNGLING Nato scientists have created a computer virus "by mistake", causing military secrets to find their way onto the internet.

The virus, called Anti-Smyser 1, was created by scientists at Nato's Kfor peacekeeping force headquarters in Pristina, Kosovo.

They were seeking protection from virus attacks similar to those launched at Nato by the Serbs during the Kosovo conflict. But the experiment went wrong, and scientists accidentally unleashed the virus on themselves.

Last week it emerged that the virus, which plucks documents from the hard drives of computers and sends invisible attachments to e-mails, recently resurfaced at the Czech ministry of defence.

"Following an investigation into the leaks, I can now tell you that this was started at Kfor by our own people and subsequently spread to Nato headquarters and to other Nato members." said Jamie Shea, a Nato spokesman.

According to Shea, Nato first became aware of the virus in December. It is now believed to be responsible for the leak in April of a restricted nine-page document detailing the rules of engagement for Nato soldiers serving in Kosovo, which appeared mysteriously on the computer screens of a London publishing company.

The document, dated December 23, 1999, set out circumstances in which "deadly force" could be used, instructed Nato troops to hand over war criminals within 48 hours to the International Criminal Tribunal for the former Yugoslavia and covered riot control, media transmissions and authorisations for everything from attack helicopters to tanks.

An e-mail with the document attached, seen by The Sunday Times, came with the following message: "Hello, I am Anti-Smyser 1. This virus is an alteration of a virus which was designed to delete all files from one's c:drive on December 13."

At the time of the leak becoming public, Shea was quoted as saying: "These are sensitive Nato documents," but last week he was keen to play down the importance of the leak.

An investigation was ordered by Nato chiefs still smarting from American allegations that a spy at Nato headquarters had leaked details of bombing plans to the Serbs during the Kosovo conflict. The claim was dismissed by Lord Robertson, the Nato secretary-general.