How Bill put us all at nuclear risk ? and saved us too

In one fell swoop, Bill Gates has both put the world at risk of nuclear attack and saved it. That is the extraordinary claim of Bruce Blair, president of the Center for Defense Information, a US non-profit military organisation. What is even more startling is that the substance of his claims is not disputed by Mr Gates's Microsoft or the US government, only the interpretation.

The story centres on a tiny bug in one of Microsoft's server software packages. Russian scientists at the Kurchatov Institute, a research organisation in Moscow, last year discovered when running the package that some files used for tracking bomb-grade nuclear material vanished from sight.

The software was donated to the Russians by the US Los Alamos Laboratory. On discovering the fault, says Mr Blair, the Russian scientists first suspected that the Americans had secretly installed a "Trojan horse" virus on the system to destabilise Russian security. But the paranoia soon subsided and the Russians contacted the authorities in the US, which is also using the same software to track its nuclear materials, to warn of the problem.

Mr Blair claims, in an article in The Washington Post, that the "fatal flaw" could have led to enough material to make thousands of nuclear weapons disappearing on to the black market.

He also says that the Russians were much more diligent record-keepers than the Americans, who didn't have a paper back-up of their files. Sorting out the problem, he says, is a "huge task that could cost more than $1bn and still might not detect the diversion of some material, should it have occurred".

In the end, of course, it didn't happen, and for a brief moment, before President George Bush came to power, the Americans and the Russians were the best of pals, happy to have averted a nuclear threat.

"The lesson is that nuclear co-operation is a two-way street, is paying off and deserves continuing support," says Mr Blair.

Microsoft and the US authorities do not deny that the bug existed. What they do dispute is Mr Blair's claims that it posed a real threat to security. But a spokeswoman for Microsoft says: "We take national security very seriously". She also confirmed that the bug in the software did result in "data loss".

She added, rather tersely: "It's a non-story because it has been fixed."

On hearing of the fault, Microsoft did indeed offer to fix the problem. But the Russian institute decided to go one better by upgrading to a newer version. But a second bug was discovered in the spanking new package.

"The [second] bug led to documentation problems," said the Microsoft spokeswoman, without being able to explain what such a fault is.

But she insisted that it wasn't as serious as the first. Phew, what a relief.