They replace critical system files with thier own. When you remove the programs, they do not undo what they have replaced. Norton is particularly bad about not being able to disable it at all, even though there is a feature that is supposed to do it. Norton and McAfee both can corrupt data files.
The overhead they add to everything you do on your computer is simply outrageous. There is no excuse for it
They are the reason why so many software companies recommend disabling them when you are downloading files.
I do not make any recommendations. I just do not use them any more. They are simply not worth the headaches to me. That is not a recommendation. I have configured my computers where they cannot get viruses based on how viruses are implanted. Most people would not go to the extremes I have as it would limit what sites you could visit (no Youtube, no flash sites, no java powered sites...) and what email you could actually read (no html of any kind, only plain text..).
