Tokyo-based Bitcoin exchange Mt. Gox lost $400 million worth of bitcoins in February. Its management said the amount was stolen after hackers exploited a transaction bug to divert the funds, but some of Mt. Gox's users are not so sure, suggesting instead that the exchange's owners pocketed the cash. Now, facing silence from those owners about the fate of the money and the methods by which 6 percent of all of the Bitcoin in the world could have been stolen, a group of hackers claims it has broken into the bankrupted Bitcoin exchange's network to get answers.

Forbes reports that the group gained access to the personal blog and Reddit account of Mark Karpeles, Mt. Gox's CEO. The hackers used the platforms to post a message that claimed Karpeles still had access to some of the bitcoins that he'd reported stolen. In support of the claim, they uploaded a series of files that included a spreadsheet of more than a million trades, Karpeles' home addresses, and a screenshot purportedly confirming the hackers' access to the data.

The hackers claim that Mt. Gox still has access to 951,116 bitcoins

Also included as part of the 716MB file was a file that appears to show the exchange's balances in 18 currencies. The hackers point to this file — which reportedly shows a balance of 951,116 bitcoins — as evidence that Mt. Gox is misrepresenting the current situation. A note in the file from the hackers reportedly reads "That fat fuck has been lying!!"

The files could simply show poor accounting practices

Forbes says the veracity of the file has yet to be confirmed. It could simply highlight the kind of poor accounting practices that allowed hackers to steal the money in the first place, showing money in Mt. Gox's balances that has long since made its way to hacker hands; or it could be evidence to support the theory that the company used the cover of a transaction exploit to steal its customers' money. The exchange claimed it had lost 750,000 of its customers' bitcoins in its bankruptcy protection filing — in addition to 100,000 of its own bitcoins — but users of the cryptocurrency are yet to see that money appear on the log of public Bitcoin transactions known as the blockchain. That would suggest whoever does have the money isn't spending it at the moment.

Forbes suggests the hack may be related to another supposed breach in which a user on BitcoinTalk's forums offered a 20GB file that they said was also stolen from Mt. Gox. The user claims the file is full of Mt. Gox users' personal details and passport scans, and that they were planning to sell it for 100 bitcoins "one or two times to make up personal losses from Mt. Gox closure."