Computers compromised by the MyDoom.O virus, which earlier this week disrupted four search engines including Google's, are being used by a new worm to launch an attempted denial of service attack on Microsoft's website.

Once a computer is infected with the follow-up Zindos worm, which spreads via the backdoor opened by MyDoom.O, it launches a denial of service attack against www.microsoft.com.

"For whatever reason, the person behind the MyDoom worm really doesn't like Microsoft," said Graham Cluley, senior technology consultant at Sophos, in a statement.

"Three minutes after a PC is infected by Zindos, it will begin to launch a denial of service attack against www.microsoft.com."

This is not the first time that MyDoom has targeted the Microsoft website. In January and February of this year MyDoom.B and MyDoom.F launched separate attacks against the software firm.

But Cluley suggested that PC owners are also to blame for the worm's spread.

"All computer users have a responsibility to ensure that their PCs are secured with up-to-date antivirus and firewall protection so that they are not unknowingly collaborating with the virus writers' illegal activity," he said.

Microsoft stated that it has taken steps to ensure that its website stays live.