According to an MT. Gox statement, a new bitcoin block too big for version 0.7 of the software was mined by miners using version 0.8, "creating a fork in the blockchain".

Miners quickly moved to downgrade to the older software until the problem is fixed and MT. Gox briefly suspended transactions.

The problem caused some temporary panic, with the currency briefly losing nearly a third of it value, dropping from more than $48 to less than $37. However, within hours it recovered to around $44.

Back in 2011 a hack at MT. Gox saw bitcoin's value crash to pennies but the currency gradually clawed back its value and has recently seen a surge as hopes rise that it could hit the mainstream.