The Dasher-B worm exploits a vulnerability in Microsoft Windows Distributed Transaction Coordinator (MSDTC), first announced by the computer giant in October. The worm opens a backdoor on vulnerable computers and causes them to connect to a remote server for further instructions. Windows 2000 computers which have not been patched are most at risk from the worm.
"Microsoft will be fuming that a virus writer is successfully exploiting another vulnerability in its operating system," said Graham Cluley, senior technology consultant for Sophos.
Microsoft has published details of the vulnerability and made patches available on its website
Sophos has warned, however, that some users were reported to have experienced difficulties with Microsoft's fix.
"The worry is that the problems with the patch may have prevented it from being successfully rolled out onto some vulnerable computers," added Cluley. "The Dasher worm wouldn't be able to spread at all if the security vulnerability in Microsoft's software didn't exist. It's important that all companies have a mechanism for rolling out security patches, as well as for automatically updating their anti-virus software."
Sophos recommends companies deploy a consolidated security system to thwart the virus and spam threats and secure their desktops and servers with automatically updated anti-virus protection, the latest security patches and properly configured firewalls.