I'm not sure what do you mean by "System" though, I use from time to time this tool. http://home.mcafee.com/Downloads/FreeScan.aspx
You mean antivirus software or what? I don't get it. If you're looking for software I suggest Avira Antivirus, it's good and free, but it has some advertisements now and then.
Cool doesn't always mean it's good, too. Benchmarks and detection rate ( positive vs. false-positive ) are simply awful.