A worm that infects computers lacking the latest security patches or updated anti-virus software is spreading rapidly, according to security experts.
The malicious program, variously known as Conficker, Downadup or Kido, was discovered in October 2008.
On its blog pages, online security firm F-Secure estimates the worm has now infected 8.9 million machines globally. However, the Finland-based firm recently suggested that the "worm virus" may be a dud.
The virus does not appearing to be working as intended, according to F-Secure. Chief security adviser Patrik Runald told PA that its coding suggests a type of bug that alerts computer users to bogus infections on their machines and offers to help by selling antivirus software. Instead, the virus is mostly spreading to little effect - though it may still pose a threat to infected computers.
Microsoft released a security patch to deal with the worm on October 23. However, computers that have not had the latest security patches installed – or which lack up-to-date anti-virus software – remain vulnerable.
"Obviously the best thing you can do - as we stressed back in November - is make sure that Microsoft’s patch is in place on every vulnerable computer on your network," wrote Sophos security expert Graham Cluley on his blog.
"In addition, you should ensure that your anti-virus software is up-to-date."
Cliff Evans, head of security and privacy at Microsoft UK, said: "Our advice is for users to ensure their antivirus protection is up to date with latest definitions. One of the ways Conficker spreads is by exploiting a vulnerability which was addressed at the end of October 2008 with Microsoft Security Bulletin MS08-067 which we further recommend users download.
"Other means of infection include exploitation of weak password policies and unprotected file shares. The easiest way to ensure latest security updates are installed is to enable the Automatic Update feature in Windows. Those that do not use Automatic Updates can go to http://update.microsoft.com.
"We have updated our customers on this threat through the Microsoft Malware Protection Center blog. We’ll continue to provide updates as necessary."
Users can download the security patch for their version of Windows from the following site http://www.microsoft.com/technet/security/Bulletin/MS08-067.mspx
Further information on the Conficker worm and how to deal with it can be found here;