And as well as this, Microsoft is re-issuing a recent security patch which has made the Internet Explorer browser crash on some computers and in so doing adds to the problem.
On 8 August Microsoft released a large collection of security patches for 23 separate flaws in Windows and programs in the Office software suite.
One of the problems discovered in the August update was considered so serious that the US Department of Homeland Security (DHS) issued a warning suggesting that users should download the security patch and apply it immediately.
Computer security firms have so far seen two types of the worm and analysis by Joe Stewart at security firm Lurhq shows that, once installed, the worm tries to download a Trojan, which can act as a spam proxy.
Fortunately, only a small number of users are thought to be suffering from the problem between Internet Explorer and the security patches. Microsoft say it affects IE with Service Pack 1 installed but only if browsing websites that use data compression and the widely used version 1.1 of the HTTP web protocols.
Microsoft said it is hoping to have the new version of the MS06-42 update ready by 22 August. A "hotfix" has been released but Microsoft said this should only be used on those computers that crash because of the update.
