Smart people don't use commercial/"well known" anti-viruses . Because actually hackers and those who design viruses/spywares know how these programmes work and their weak ponits. So don't believe that your computer is clean when they say so. I'm starting to think that Norton is a virus itself.
I personally use
Kaspersky , it works as an Anti-virus , firewall and anti everything you can imagine and I think it's the best one i've had yet . It works perfectly 1000% ,it doesn't make your computer FAT-BITCH like Norton and it detects EVERYTHING .