I know people put their faith in programs like McAfee, but having done a little freelance tech support and been to dozens of people's homes, I have very little faith in them, and tend to believe that they do more harm than good.

If you can manage it despite the slowness, I'd seriously recommend temporarily uninstalling McAfee, loading AVG Antivirus, and seeing if you notice an improvement. There were several instances I've seen that McAfee uses so many system resources that it makes the computer unusable. When weighed against your average virus, I actually find that more damaging!

And I must post this once and for all. Like I said, I've been to dozens of people's homes to work on their computers. Once I got a job I stopped. However, from that experience I noticed an interesting thing. There hasn't been a computer yet on which I haven't found at least one virus with AVG where Norton or McAfee said there was none. Half of these instances resulted in some semi-nasty viruses. Now, this isn't to say it can't work the other way around, but I think that when all the pros and cons are weighed, AVG has far more going for it.