Many, but not all, AV vendors participate in these scanners. Last night, Ziv Mador at Microsoft announced that Microsoft will be joining VirusTotal.
Hi, this is Ziv Mador again from the Microsoft Anti-Malware team. This week, the folks over at VirusTotal added the Microsoft anti-malware engine to their service. VirusTotal is a free service that enables users to submit suspicious files to be scanned by several anti-malware engines. If you choose, files that are not identified as malicious are sent to the vendors who supply the anti-malware engines to this service to be analyzed. As of April 27, the Microsoft anti-malware scanner is included in the set of scanning engines used by VirusTotal. This scanner is based on the same technology found in Windows Live OneCare, the Windows Malicious Software Removal Tool, and Microsoft Antigen, and includes our full antivirus set of signatures. We are glad to be participating in this community opportunity.
(Hat Tip to Jose)