Morris worm

Robert Tappan Morris, a Cornell graduate student, launched it on 2 November 1988 from a machine at MIT. It went after VAX and Sun systems running BSD and had three ways in: a buffer overflow in fingerd, the debug mode in sendmail, and the trust relationships of rsh, backed up by guessing weak passwords.

The stated goal was to measure the size of the network. A flaw in its logic made it reinfect the same machine over and over until the host buckled under the load. Estimates put the damage at a few thousand of the roughly 60,000 connected computers. Morris became the first person convicted under the Computer Fraud and Abuse Act, and DARPA responded by funding CERT/CC at Carnegie Mellon. He later co-founded Y Combinator and became a professor at MIT, which is one way to recover from a bad first impression.