Suspicious files in my Windows

While I am doing a quick scan for virus on Norton 360, I noticed a long stop at some files. Their names are very very suspicious. Although I can't recall all of them, one of them, which I clearly remember, is Backdoor.Rustock.A. I searched this on the Internet, and the results are... Pretty shocking. It turned out to be a little virus-like stuff. I tried to remove it but, I can't even FIND the file. Why does Norton skips that file instead of treating it like a virus and removes it? What should I do to remove it, or is it even harmful?

Thank you!