Used to get a virus or a trojan or just some annoying malware all the time, despite running AVG, ZoneAlarm, and regular sweeps with the usual free malware remover programs from a few years ago. It was the family computer, you see. My little brother once got us over 400 viruses, trojans, etc. in just a few hours after installing Kazaa. And of course, since I was the only one remotely familiar with cleaning stuff up, it was always up to me to try and keep things tidy.
That was back when I used Windows XP (and before Vista was released). I moved the family computer over to Ubuntu and have practically forgotten what it's like to run malware scans every other day.