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13 Aug 2006

Worms exploit critical MS06-040 Microsoft security vulnerability

Companies urged to roll-out security patch as a matter of priority

The worms exploit a critical Microsoft security vulnerability
The worms exploit a critical Microsoft security vulnerability.

Experts at SophosLabs™, Sophos's global network of virus, spyware and spam analysis centers, have warned computer users of malware that is exploiting a critical security vulnerability in Microsoft software.

The W32/Cuebot-L and W32/Cuebot-M worms spread via AOL instant messenger, exploiting the vulnerability described in Microsoft's MS06-040 security bulletin.

"Microsoft only issued a patch against the security hole used by these worms in the last few days, and yet already malware is being written that exploits this vulnerability to attack computer systems. This is a real headache for Microsoft as they try and reassure people that their operating system is becoming more secure," said Graham Cluley, senior technology consultant for Sophos. "There will be many Windows computers that will not have been patched yet and may be vulnerable to infection and compromise. We wouldn't be surprised if more worms were released which exploited this security hole in Microsoft's software. Everyone should act swiftly to ensure their PCs are properly protected with anti-virus software, firewall software and up-to-date security patches."

Once the Cuebot-L or Cuebot-M worms have infected a PC they turn off the Windows firewall and open a backdoor, allowing remote hackers to gain access and control over the computer.

Sophos advised customers to patch against the latest security vulnerabilities in Microsoft's software last week.

Home users of Microsoft Windows can visit to have their systems scanned for critical Microsoft security vulnerabilities.

Sophos suggests that every IT manager responsible for security should consider subscribing to vulnerability mailing lists such as that operated by Microsoft at

Sophos continues to recommend companies protect their desktops and servers with automatically updated protection against viruses, spyware, and spam.

About Sophos

More than 100 million users in 150 countries rely on Sophos as the best protection against complex threats and data loss. Sophos is committed to providing complete security solutions that are simple to deploy, manage, and use and that deliver the industry's lowest total cost of ownership. Sophos offers award-winning encryption, endpoint security, web, email, mobile and network security solutions backed by SophosLabs - a global network of threat intelligence centers.

Sophos is headquartered in Boston, US and Oxford, UK. More information is available at