alt Hacker NewsThe 10% number is completely made up. According to Paul Graham, "I was there when this statistic was cooked up, and this was the recipe: someone guessed that there were about 60,000 computers attached to the Internet, and that the worm might have infected ten percent of them."
That figure is probably UUCP mostly not live connected hosts. I could be wrong, but 60k hosts that you could telnet to sounds like a lot of ducking hosts back then. I was there too, in my late teens. God bless PG.