2. Worm Goes Wild

Robert Tappan Morris developed a program in 1988 when he was a student at Cornell University. What he believed as a harmless experiment spread wildly, crashing thousands of computers because of a coding error. It was the first widespread worm attack. Morris, who now is the co-founder of the startup incubator Y Combinator and a professor at the Massachusetts Institute of Technology, was convicted of criminal hacking and fined $10,000. His lawyer claimed at the trial that his client's program helped improve computer security. Costs for cleaning up the mess may have gone as high as $100 million.

3. Patriot's Fatal Error

In February of 1991, a U.S. Patriot missile defense system in Dhahran, Saudi Arabia, failed to detect an attack on an Army barracks. This was caused because of a software problem which led the system to inaccurately track calculation. This problem grew when the operated for long. On the day of the incident, the system had been operating for more than 100 hours, and the inaccuracy was serious enough to cause the system to look in the wrong place. This resulted in the loss of lives of 28 American soldiers.