Microsoft's free security tools don't get the respect they deserve, but they're actually good performers. Take the Windows Malicious Software Removal Tool. This small, portable utility checks Windows XP, 2000, Server 2003, Vista, and 7 for infection by a range of known threats, including Blaster, MyDoom, and Sasser, and removes any threats it finds. Microsoft is quick to point out that the Windows Malicious Software Removal Tool is no substitute for antivirus software. It doesn't protect your system from infection; it merely finds and removes any known threats. It's available in separate downloads for 32-bit and 64-bit Windows versions, but the tool won't let you use the wrong version so there's little risk of getting it wrong. This program is fully portable, so it can run on any compatible Windows machine without having to be installed.
The Windows Malicious Software Removal Tool is utter simplicity to use. Its dialog-style interface offers three scan options: Quick, Full, and Customized. The Quick scan targets those areas most likely to be infected by malware. If none is found, the tool prompts you to run a Full scan, which scans your entire system thoroughly but can take several hours on large systems. The Customized scan performs a Quick scan and also scans user-specified folders. We started with the Quick scan. A green bar graph tracked the tool's progress as it rapidly scanned critical areas of our C drive. The Quick scan took less than a minute and found no malicious software, though we could view detailed results anyway, if we wanted to. But we moved on the Full scan. This took much longer, of course, but it was worth it to be sure than no crudware lurked in our system's deep dark corners.
Obviously Microsoft didn't waste a lot of resources on a zooty interface or a snappy market-tested name for this simple but effective scanner and cleanser, but it does release an updated version of it on the second Tuesday of each month. We strongly recommend downloading and running the latest version now and then, and every few months at a minimum.