I got a couple of viruses between the time my 90 day Norton (which came with the computer) expired, and I loaded Norton System Works. I went to Symantec's site, downloaded the repair for the two viruses, and ran them. It took quite awhile to do the repairs, especially for the computer challenged like myself, but afterwards I installed the complte Norton, and set it up to do updates. Haven't had a virus since.
I also wont open emails from anyone I don't know. I simply delete them. I think that helps avoid viruses also. I know I got one from an AOL email user that was titled AIMgunny@aol.com Whoever this terrorist was tried over and over to infect my computer with this same virus, but finally gave up after about a week. I guess he didn't know it worked the first time, and I had fixed it, so he kept trying.
Anyway, Norton really works for my computer.