According to a note released to Microsoft MVPs (Most Valuable Professionals), the initial version of the tool, code-named Titan, will be able to detect and delete the Blaster, Sasser, MyDoom, DoomJuice, Zindos, Berweb/Download.Ject, Gailbot and Nachi viruses.The tool will be updated on a monthly base. But Microsoft said that in the event of a major virus or worm outbreak it will push make updates available outside of the monthly cycle
More info at eWeek