This was actually announced April 27th but for those who missed it can read the news here.

The Malware Team at Microsoft announced earlier that the people at VirusTotal added Microsoft's Antimalware engine to their service. For those who are not aware of VirusTotal, it's a free service than enable users to submit suspicious files and to be scanned by several antimalware engines. The scanner is the same technology that Windows OneCare and Windows Malicious Software Removal Tool use.

http://www.virustotal.com/en/indexf.html