This happened on August 1, 2012.

Knightmare: A DevOps Cautionary Tale

During the 45-minutes of Hell that Knight experienced they attempted several counter measures to try and stop the erroneous trades. There was no kill-switch (and no documented procedures for how to react) so they were left trying to diagnose the issue in a live trading environment where 8 million shares were being traded every minute.

Knight Capital Group realized a $460 million loss in 45-minutes. Remember, Knight only has $365 million in cash and equivalents. In 45-minutes Knight went from being the largest trader in US equities and a major market maker in the NYSE and NASDAQ to bankrupt. They had 48-hours to raise the capital necessary to cover their losses (which they managed to do with a $400 million investment from around a half-dozen investors).