Less than 5 minutes after the unmanned Mariner 1 spacecraft launched on July 22, 1962, another rocket launched by NASA destroyed it. Mariner's navigation code malfunctioned, making it impossible to navigate the craft, so NASA destroyed it before it could crash-land on earth. The problem? A missing hyphen in Mariner's code responsible for transmitting navigation instructions...
7. JP Morgan Chase & Co., 2012
The London Whale fiasco -- in which JPMorgan lost $6 billion on a credit-derivative bet gone wrong -- isn't just the story of poor supervision and greedy traders. It's also the story of bad spreadsheets leading to worse results. When it came time to implement a new model to calculate the risk of the trade at the heart of JPMorgan's historical loss, the man in charge of doing the calculations from spreadsheets with trade data made a mistake: Where he was supposed to divide by the average of the new and old "hazard rates," he divided by the sum, according to the U.S. Senate's report. The report claimed that this error understated the volatility in the new calculation by a factor of two and ended up lowering the trade's reported risk.
http://www.bloomberg.com/news/2013-04-17/7-data-disasters-more-embarrassing-than-reinhart-and-rogoff-s.html