Microsoft Safety Scanner Free Tool
The Microsoft Safety Scanner is a free tool that can remove viruses, spyware, and other malicious software and runs with your existing antivirus software but it is not a replacement of an antivirus software program that provides ongoing protection. In fact, it expires after 10 days after being downloaded.
Download the tool from here - http://blogs.msdn.com/b/robmar/archive/2011/04/14/download-microsoft-safety-scanner.aspx
How to troubleshoot an error when you run the Microsoft Safety Scanner - http://support.microsoft.com/kb/2520970