A user account carrying a significant amount of Bitcoin on the trading site Mt. Gox was hacked by an unknown party. The hacker then attempted to sell the lot to themselves and exchange the Bitcoin into US dollars. Mt.Gox shut down for the day and is rolling back all trading to it’s state before the breach. It’s still undetermined who was responsible for the hack, but the IP address originated out of Hong Kong. All users will be forced to reauthenticate their accounts.”]
Source: https://gizmodo.com/bitcoin-price-tumbles-after-massive-account-hack-and-se-5813622