The Morris worm was a worm accidentally released into the Internet by Robert Tappan Morris. The worm was supposed to be innocuous, but because of a programming bug it fatally crippled its host. The end result of the worm was to disable 10% of the Internet at that time (60,000 servers).
What would happen if 10% of the Internet today went down? Catastrophe!
I can remember reading about it in the newspaper and on Usenet and elsewhere, and following the details. I can remember the talk about young rtm (his login) and his father, a security expert for the National Security Administration (or NSA).
There is an article in Network World about this event that is worth reading.