Personal opinion only.
I hate Norton with a passion and believe it can slow your computer up.
I much prefer a selection of FREE utilities that come with excellent recommendations. At the moment I use:
Comodo Firewall
Avast Anti virus
AVG anti-spyware (not the AVG antivirus)
These programs have automatic updates.
I also run on a regular basis:
A2
AdAware
Spybot
All free.
But other people will have very different ideas and some will prefer Norton. I suggest you download either A2, AdAware, or Spybot (or all of them!) and see if they find anything.
A2 Free 3.0 (The second in this list)
http://www.emsisoft.com/en/software/download/
AdAware
http://www.filehippo.com/download_ad-aware/
Spybot
http://www.filehippo.com/download_spybot_searc h_destroy/