1:56pm UK, Friday August 15, 2003

Microsoft is waiting to discover whether action taken to stop the Blaster worm virus crashing one of its most important websites has been successful.

The virus is programmed in such a way that infected PCs worldwide will bombard the Windows Update website at midnight.

180 blaster virus worm microsoft

Microsoft staff

With different time zones around the world, it could mean the damage beginning at any time.

Expertsbelieve up to half of the world's computers may be infected.

Stuart Okin, chief security officer at Microsoft UK, said: "My hope is that all the steps we have taken will be adequate.

"I can't go into details for security reasons but we have made contingency plans.

"My personal belief is that this particular worm is not going to be that effective."

Even so, the software giant says the worm is one of the most serious viruses it has ever faced.

Windows users have been urged to download a special "patch" designed to disable the worm and prevent computers sending the potentially damaging data.

Microsoft officials are worried about variants of the worm which may have infected computers without the owners' knowledge.