There are a variety of one-time scan tools available for free, that will check your system for baddies. I’ve previously blogged about ADWCleaner and Norton Power Eraser, and now I should mention McAfee Stinger.
McAfee Stinger is a quick scan for your PC that can detect and remove a specific set of viruses and trojans. If you have reason to think you’re infected, you can download Stinger and use it anytime. It won’t conflict with your full-time antivirus, and it won’t try to sell you anything.