17 September 2003 Another large-scale attack against Microsoft Windows-based PCs and servers is expected within days, after security specialists said that hackers were distributing a ‘crack’ to exploit a new vulnerability, reported last week.

It follows an admission by Microsoft that the patch it issued in July to protect PCs and servers against the Blaster worm, did not fully fix the flaw in its operating systems — Users of Windows 95, 98 and Millennium Edition (ME) are not affected.

Since then, Microsoft has released another patch, but the company and security experts are concerned that too few users have downloaded it — leaving millions of PCs and servers around the worldwide vulnerable once again.

The new vulnerability could, like that exploited by the Blaster-A worm, allow a remote attacker to run code on a user’s system, warned anti-virus software vendor Sophos.

Security consultancy iDefense said that cracking tools had already been uncovered on a Chinese web site. Ken Dunham, a senior analyst at iDefense, said that the tool had already been deployed by some hackers.

The warning came just a day after Microsoft CEO Steve Ballmer gave a speech to the Churchill Club, a Silicon Valley executive group, in which he promised that Microsoft would take a “laser focus” on security in a bid to make good the company’s poor record.

But he had added: “This is not a problem that will go away overnight.”