How do I keep my computer safe?

I was thinking about this today. I'm not sure what kind of anti virus software we have on our laptop. Heck, I don't even know if we have anything. Yeah I know that is just crazy. We do have to have something. If I remember correctly we had Norton on our desk top. I guess it worked well. I'll have to ask Michael what we have on the laptop. My fear is just that we are going to get a horrible virus and lose all of our pictures of the kids. We do have several of them saved to discs, but I'm sure there are almost as many not saved yet. I would hate to lose all that stuff.