The thing about antivirus software screwing up your system is especially true for the latest versions of Norton. I used to have McAffee years ago and it was good. Now I use AVG on Windows and F-Prot on Linux. But it's true that no program can detect ALL existing viruses.
Leon-IH, school gives you knowledge and some experience, but not intelligence. I'm not saying you're not intelligent, just that you won't get smarter by going to school. On the other hand, the more you use your mind for something, the easier it becomes.