clipped from: www.computerworld.com   
The computer worm that exploits a months-old Windows bug has infected more than a million PCs in the past 24 hours, a security company said today.

Early Wednesday, Helsinki, Finland-based security firm F-Secure Corp. estimated that 3.5 million PCs have been compromised by the "Downadup" worm, an increase of more than 1.1 million since Tuesday.

"[And] we still consider this to be a conservative estimate," said Sean Sullivan, a researcher at F-Secure, in an entry to the company's Security Lab blog. Yesterday, F-Secure said the worm had infected an estimated 2.4 million machines.

The worm, which several security companies have described as surging dramatically during the past few days, exploits a bug in the Windows Server service used by all supported versions of Microsoft Corp.'s operating system, including Windows 2000, XP, Vista, Server 2003 and Server 2008.

Microsoft issued an emergency patch in late October, fixing the flaw with one of its rare "out of cycle" updates.