Morris

The Morris worm or Internet worm of November 2, 1988, was one of the oldest computer worms distributed via the Internet, and the first to gain significant mainstream media attention. It also resulted in the first felony conviction in the US under the 1986 Computer Fraud and Abuse Act. It was written by a graduate student at Cornell University, Robert Tappan Morris, and launched on November 2, 1988, from the computer systems of the Massachusetts Institute of Technology. [...] Though Morris did not intend for the worm to be actively destructive, instead seeking to merely highlight the weaknesses present in many networks of the time, an unintentional consequence of Morris's coding resulted in the worm being more damaging and more easily spread than originally planned.

Morris's coding mistake, in instructing the worm to replicate itself regardless of a computer's reported infection status, transformed the worm from a potentially harmless intellectual and computing exercise into a viral denial of service attack. [...] The U.S. Government Accountability Office put the cost of the damage at $100,000–$10,000,000.