I have installed Norton’s Internet Security software on a few computers, and in my experience, while Norton makes good software, Norton significantly reduces your PC’s performance. And then there’s the price of the software, and the subscription fees. If you’re tired of Norton or McAfee chewing up your computer’s resources (and your money), download AVG’s free anti-virus software. I also recommend educating yourself about rootkits and how they can hide various nefarious infections from your plain view and from solid anti-virus software. After reading about rootkits you may want to download something like IceSword (for advanced users), which is a free anti-rootkit program, or RootkitRevealer. Note: you should have Microsoft Automatic Updates turned on, and thus you should have Microsoft’s Malicious Software Removal Tool already installed.
Or, if you want to believe Apple and their claims that Mac users are relatively free from worries about computer infections, then buy a Mac, but be prepared to spend a lot more money, a ton of time learning a new operating system, and plenty of frustration on top of that.