When i was 10 years old i got infected over msn by a worm. It was kinda hard to delete it as i had no anti virus scan. And the worm didnt lets me go on internet.
I create viruses and worms, and botnets, I created the first dcom worm, which spread to over a million computers in less than 3 days, I had control of every single pc..
Personally I think the worst virus I have ever been infected with would be a RAT. Reasons being obvious I hope, such as the fact that it has almost everything a skid needs.