Mt. Gox, still the world's largest Bitcoin exchange, suspends all Bitcoin withdrawals citing a bug known as "transaction malleability." The announcement sends shockwaves through the market and marks the beginning of the exchange's final collapse. Behind the scenes, 850,000 BTC are already missing. Over the next two weeks, the situation deteriorates rapidly -- leaked internal documents reveal insolvency, and Mt. Gox shuts down entirely on February 24, 2014.
Wikipedia: Mt. Gox