Microsoft has launched a free antivirus tool with latest virus definition. It requires no installation. Only copy and paste the tool in your system and run the file. If it detects any virus or malwarem, it will be quarantined. Download this tool from original Microsoft download website.
Microsoft Safety Scanner is available as a free download for both 32-bit and 64-bit version of Windows. It works fine on Windows XP, Windows Vista and Windows 7.
This tool does not perform any check for genuine Windows. This software expires after 10 days. So download this after each 10 days with lates virus database.