'Huge increase' in worm attacks plague unpatched Windows PCs

A computer worm that exploits a Windows bug Microsoft Corp. patched more than two months ago continues to wreak havoc, a security company said Monday, as it boosted its overall threat ranking and warned users to patch their PCs.

"We've seen a huge increase in the number of [malware] samples, as well as infections," said Ryan Sherstobitoff, chief corporate evangelist at Panda Security, referring to the "Conficker.c" worm.

In response, Panda upped its Global ThreatWatch to "orange" status, a move that means the company believes users face "an important danger."

The worm, which was first reported by Panda and other security companies on Dec. 31, 2008, exploits a vulnerability in the Windows Server service that's part of all currently supported versions of Microsoft's operating system, including Windows 2000, XP, Vista, Server 2003 and Server 2008.

Microsoft issued an emergency patch Oct. 23 to fix the flaw with one of its rare "out of cycle" updates.

Conficker.c, said Sherstobitoff, pings machines with malformed RPC (remote procedure call) packets in the hope of finding PCs not yet patched with the October update. The worm can also spread via brute-force attacks against systems' usernames and passwords, and from an infected PC to a USB-based device, such as a flash drive or digital camera, on which it then hitchhikes to another computer.

Once on a system, the worm downloads new versions of itself from a rapidly changing list of malicious Web sites, tries to block most security software updates, and installs more malware on the machine.

"The biggest issue is replication over the network," said Sherstobitoff, who added that the USB attack vector, while serious, has so far played just a small part in the overall picture.

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