Seriously, Mom, It’s Not Always a Virus
I know the baby pictures are slow to download today, but that's because my sister sent them to you as 12MB files instead of shrinking them as she should have. It's an honest mistake, and it doesn't mean you have a virus.
The last time I was home (great turkey, BTW), I made sure your antivirus software was up-to-date, and your subscription still has six months to go. You're running regular scans each weekend, and I'm sure that even if you did something dumb like click on a "Taylor Lautner Shirtless Picture" e-mail, your antivirus system would have caught anything bad that might have happened.
In fact, if your computer feels slow, your antivirus software is almost certainly responsible to some extent: It runs in the background all the time, and you shouldn't turn it off. But if things feel slower than usual, it's probably because you have 11 applications and 18 Web browser windows open, and because you haven't rebooted your machine in three weeks. (Even if you do shut down those programs, memory may not be released properly--Firefox is notorious for this.)
So shut everything down. Reboot. And if things still feel slow, try some of the tips in "Software Speed Boosts for Your PC." I'm sure we can get things back to speed in no time.
And no, your computer can't get sick if you sneeze on the keyboard.