antivirus
I wondered what you do online? And how fluent are you with computers?
I use Trend Micro, its great. But I wouldnt recommend it to someone not familiar with computers or the internet. Trendmicro has LOADS of great features, like web site blocker, unauthorized change prevention, a great firewall, parental controls (I use parental controls to keep advertisement sites and porn sites from coming up) and lots more that I dont want to have to list.
If you are more of a casual computer user, then I'd recommend the "Free AVG". My fiancee has that and she hasn't had any problems.
Trend Micro has had some problems over the years I've had it, but its well worth it. But so has AVG for that matter. Though AVG is free.
I run antivirus scans about once a week and then run a fast scan with MalwareBytes AntiMalware. I haven't ever caught anything other than a cookie or two that lingered in I.E. (I hate I.E.).
I also highly recommend "BetterPrivacy" addon for Firefox to everyone out there. Click here to check it out:
https://addons.mozilla.org/en-US/firefox/addon/6623
And HPVISTA, if you arent using FireFox, then you should be.