The mass-mailing worm spewing thousands of hate mail messages has been stopped, according to German security researchers.

The researchers found that the Sober worm was preparing to go dormant on Monday and restart its activities on Thursday.

But researchers analyzing the worm discovered the web sites feeding it new code, and with the cooperation of many Internet service providers were able to shut those sites down.

The worm may reside on thousands of PCs worldwide, and on Thursday it may again try to send messages from those compromised machines.

The nuisance worm affects PCs running the Windows operating system, from Windows 95 through Server 2003. Security experts advise users to update antivirus software regularly.