Jeff Jones, a senior director at Microsoft, described the problem as similar to that which spawned the Blaster internet worm last month.

The worm, which also operated as MSBlast and LovSan, crashed many of the computers it infected and tried to bring down Microsoft’s website. Mr Jones said that hackers had yet to target the new security flaw but advised customers to download a new program from the software giant’s website to repair the fault.

“We have a worry that history has shown us there are malicious individuals out there that could create an attack of some sort against it,” he said.

The company said that Windows NT 4.0, Windows 2000, Windows XP and Windows Server 2003 operating systems could be affected by the flaw.

Software consultants last night gave warning that the flaw would goad potential hackers into devising a new virus.

Marc Maiffret, a consultant at eEye Digital Security, which discovered the latest flaw, said: “I can’t even imagine the frustration level administrators will be feeling today.”

Central Command, a virus protection company, said that Microsoft’s previous security alert was the catalyst for the last attack by hackers on its software but said the company had little choice but to alert its users. Steven Sundermeier, vice-president at Central, said: “It’s a double edged sword. You have to let corporations know so that they can protect themselves.”

Since early last year, Microsoft has made software security a top priority in an attempt to address rising customer concerns about the spread of viruses and hacker attacks.