I am sorry Norton either didn't work for you or didn't bother to configure
its numerous settings properly.

Rememeber you people attacking me for not knowing "how to use" Vista?

Fact is Norton was good to me, it did take a few googles to find solutions
to its quirky issues - NETWORKING (get disabled when certain Symantec
services is disabled), other than that, I'd be tearing my hair out in
January 2009 when it saved me from disaster in Safe Mode.
I couldn't destroy slowly spreading infection, until I ran NortonAV in
SafeMode and Lord, it found one of THEE most dangerous viruses in the world
on my machine.

Free AV tends to be less powerful because people writing it are motivated
only by good will and maybe semi-government organization, when money gets
involved, product improves.
If money were involved in Linux it wouldn't be a "hobby OS".

Your Avast, etc are hobby AV's.