I dunno if that Spybot is well to catching the nasty. For example; it alert me that Windows Update is downloading on my computer. It should be trust brand company but I don't understand that one for now. About the Norton that I learned and their product tend to hog over the memory's space made little bit slow.
I remember in past that I read about Anti Virus the from expert advise that said important look at their software that how much will using the RAM (Memory). Also there are public that can play with all kind of viruses to test and see if the anti virus pick up the nasty.
Today the server of collection viruses no longer for public.
However I think PC Cillin is best.