Microsoft has launched a new, free virus/malware scanner, that's designed to be used if you think your computer might be infected.
The program is called the Microsoft Safety Scanner. To use it, download the file from http://www.microsoft.com/security/scanner/en-us/default.aspx and then run it on your PC. The app is portable, so doesn't need an installer. When you run it, it will analyze your computer and detect, and remove, many of the most prevalent viruses.
Microsoft points out that this on-demand tool is not a substitute for a proper on-access antivirus product. It's simply designed to be used in emergencies, such as if you think your computer may have a problem that has managed to sneak past your existing defences. Also, note that the program automatically expires after 10 days, so if you want to run it regularly you'll need to keep downloading the latest version.
At first glance, Safety Scanner is a welcome addition to Microsoft's range of free security tools, of which its Security Essentials suite is probably the best known. But at 67 MB for the download, for a program that expires after 10 days, we can't work out why it needs to be so huge. McAfee offers a similar product, which is also free, called Stinger. It doesn't expire after 10 days, can be downloaded from http://www.mcafee.com/us/downloads/free-tools/how-to-use-stinger.aspx, and runs to just a 7.7 MB download.