As is its custom, Microsoft updated its Windows Malicious Software Tool Tuesday as part of the monthly security bulletin roll-out, adding detection and deletion routines for four additional worm families.

The free-of-charge tool now seeks and destroys the Spybot, Kelvir, Mytob, and Lovgate malware clans. Windows XP and Windows Server 2003 SP1 users who have Automatic Update enabled automatically receive the tool each month, while those using Windows or Microsoft Update also get the utility as part of any update package. Windows 2000 and other Windows Server 2003 users, however, must manually download the tool from the Microsoft Web site or use the online edition.

The addition of Kelvir and Mytob are particularly important, as both those families account for scores of variants, including several that have hit the Internet in just the past few days.

Since Sunday, for instance, security vendor Symantec has tracked 11 different Mytobs and 3 new Kelvirs.