I’ve discovered an excellent alternative to Norton Antivirus. It’s called AVG Antivirus, and they even have a free version.
You can download the setup file here. The free version does require a serial number (not sure why), so here it is: AVG-1-21978805-MKL.
Please note that I am only putting this on here, because their registration process is a pain in the rear, and if you’re using hotmail, or some other poor excuse for an email provider, it might take quite a while to get emails from them. Fortunately I don’t have that problem, since I use postmark.net.