Microsoft urges home users to blast MSBlast

Microsoft released a removal tool for the MSBlast worm on Monday after ISPs complained that home users' PCs infected with the malicious program are still causing network congestion.

The MSBlast worm, also commonly called the Blaster worm, started spreading last August and is believed to have spread to hundreds of thousands of systems. While most corporations have cleaned up the worm, Microsoft has found that a large number of home users are still unknowingly infected, the software giant said in a statement.

"For many users in this situation, there is little indication that they are infected other than possible performance degradation," Microsoft said in a statement. "And those infected are still actively transmitting the worm, causing internet congestion in the process."

Worms - programs that spread between vulnerable computers over a network - have been the bane of Microsoft since Code Red and Nimda hit computers running the software giant's operating system in summer 2001. Nimda, which hit computers a week after the 11 September 2001 terrorist attacks, put the company on the path toward making security its number one priority. Four months later, Microsoft announced its Trustworthy Computing Initiative to do just that.

However, Microsoft developers have had their work cut out for them. Despite a Windows work stoppage of more than two months while programmers reviewed the code, security flaws continue to crop up and be exploited by malicious worm writers.

A year ago, the Slammer worm spread quickly among Windows servers and devices that had Microsoft's SQL database software installed. And the MSBlast worm abused a 23-day-old vulnerability to spread in August and September.

Microsoft has since set up a site called Protect your PC to help home users lock down their computers and posted a $250,000 bounty for the writers of the MSBlast worm and the SoBig.F virus.

Microsoft's aim in releasing the latest tool is to reduce the amount of traffic being born by ISPs by cleaning up a significant number of home computers.

The tool can be found on Microsoft's download site.

Robert Lemos writes for CNET News.com.