Separate groups of hackers are releasing a barrage of worms in a battle to seize control of Windows PCs that remain vulnerable to the now infamous Windows Plug-and-Play vulnerability.

The Bozori worm attempts to remove infections by earlier versions of the Zotob worm and other malware, so it can take control of a compromised computer for itself. A family of IRC bots that exploit the same Microsoft (MS05-039) Plug and Play vulnerability likewise try to remove competing PnP bots, as explained in a diagram by Finnish anti-virus firm F-Secure here. It reckons 11 different types of malware are exploiting the vulnerability.

The upswing in malware creation - and competition between various PnP worms - echoes the competition between NetSky and Bagle worms for control of vulnerable Windows PCs that first flared up in March 2004. Then, as now, it's all about turning Windows PCs in zombie spam bots.

"Once one of these worms has control over your computer, it can use your PC for sending spam, launching an extortion denial-of-service attack against a website, stealing confidential information or blasting out new versions of malware to other unsuspecting computer users," said Graham Cluley, senior technology consultant at Sophos. "Organised criminal gangs are behind attacks like these and their motive is to make money. Owning a large network of compromised computers is a valuable asset to these criminals, and every business needs to take steps to ensure they are not the next victim on their list."

The worms are affecting computers which are not properly patched against Microsoft security holes such as the MS05-039 Plug and Play vulnerability, disclosed by Microsoft last week. Windows 2000 systems are particularly at risk of exploit. Many organisations have already been hit including CNN, ABC, The Financial Times, and the New York Times. General Electric, United Parcel Service, Caterpillar and the US Congress have also been affected by PnP worm infestation.

Security firms at odds over seriousness of outbreak

This sounds bad but according to Russian anti-virus firm Kaspersky Labs the seriousness of the outbreak has been exaggerated by the media. "There has not been any noticeable increase in network activity which could be ascribed to this worm [outbreak]. During the Sasser epidemic in May 2004, which some publications are using as a comparison for Bozori-A, Sasser caused an increase in network traffic of approximately 20 per cent to 40 per cent. At the moment, there are no signs of a similar increase," it said. Kaspersky's argument has been bolstered by a lowering of the alert status at Internet Storm Centre (ISC), which runs a well respected vendor-independent syber threat monitoring and alert system.

However security firm Arbor Networks takes the opposite line and said that, if anything, the Zotob Worm is being underestimated. "Arbor Networks has received calls from a number of large companies that have been devastated by Zotob. Because there have been an additional seven variants of the worm released and the most recent one is through email, this has the potential to become a much bigger problem for companies," it said.

"This worm is picking up new tricks along the way, leveraging old exploits and has become a multi-vector, blended threat. This is an indication of the amount of code sharing that takes place among worm and malware authors."

Although vendors differ over the scope of the attack there's general agreement over remedial actions: block traffic on port 445 at least at the internet perimeter, patch systems quickly, apply anti-virus signature updates. Tin-foil hats may not go amiss either. ®