Bitcoin is facing the biggest test of confidence in the nascent virtual currency, after its oldest and most famous exchange went dark and customers feared the loss of $400 million worth of Bitcoin.

Mt Gox exchange suddenly deleted its Twitter history and pulled its website offline yesterday. A document circulated online alleging that the exchange had lost 744,000 Bitcoins – almost 6 per cent of the 12.44 million coins in circulation – in "theft" by outside hackers.

Mt Gox made no comment on the allegations. But while it is unclear what happened, the exchange’s customers were coming to terms with the likelihood they will not see their funds again. – Copyright The Financial Times Limited 2014