On those occasions where you think something maybe wrong, then you should use an alternate tool to make sure that your current tools are not missing something. Check out Microsoft's new Safety Scanner it's a free downloadable security tool that provides on-demand scanning and helps with the removal of malware. It also works with your existing anti-malware software.
Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To scan your system with the latest anti-malware definitions, all you need to do is re-download and run the Safety Scanner again.The Safety Scanner is not a meant as replacement for using an real-time anti-malware software program that provides ongoing protection. For free real-time malware protection download Microsoft Security Essentials.