Mt. Gox, the Tokyo-based bitcoin exchange that halted withdrawals this month, wentoffline as a document surfaced alleging long-term theft of about$365 million in the digital currency.

A document posted online that appeared to be an internalstrategy paper said unidentified thieves stole 744,408 bitcoinsfrom the exchange—about $365 million at current rates—and that thetheft “went unnoticed for several years.”

“The reality is that Mt. Gox can go bankrupt at any moment, andcertainly deserves to as a company,” according to the document.

The document, which outlines plans for leadership changes,re-branding, and a possible move to Singapore, was posted online byblogger Ryan Galt. A person briefed on the situation at Mt. Gox,who asked to remain anonymous because the document is private, saidhe believed it is authentic.

Bitcoin fell 5 percent to $517.71 at 4:48 p.m. London time,according to the CoinDesk Bitcoin Price Index, which averagesexchange prices. That's down from as high as $1,151 on Dec. 4.

Mt. Gox went offline to “protect the site and our users,”according to a statement on its website. “We will be closelymonitoring the situation and will react accordingly,” it added.

'Tragic Violation'

A group of bitcoin-related companies sought to distancethemselves from Mt. Gox, and promised to protect customer funds topromote usage of the currency.

“This tragic violation of the trust of users of Mt. Gox was theresult of one company's actions and does not reflect the resilienceor value of bitcoin and the digital currency industry,” SanFrancisco-based Coinbase said in a joint statement on its websitewith Kraken, BitStamp, Circle, and BTC China, other prominentbitcoin-related companies.

“As with any new industry, there are certain bad actors thatneed to be weeded out, and that is what we are seeing today,” thecompanies said in the statement.

Efforts to reach the www.mtgox.com website earlier todaydirected users to a blank white page, a day after Mt. Gox ChiefExecutive Officer Mark Karpeles resigned from the BitcoinFoundation, an advocacy group for the digital money. At one pointtoday, the site read “put announce for mtgox acq here.”

“We are shocked to learn about Mt. Gox's alleged insolvency,”the foundation said in an emailed statement.

Bitcoin was introduced in 2008 by a programmer or group ofprogrammers under the name Satoshi Nakamoto and has since gainedtraction with merchants around the world. The digital money, basedon a peer-to-peer software protocol, has no central issuingauthority and uses a public ledger to verify transactions whilepreserving users' anonymity.

The Bitcoin Foundation said that, despite the troubles at Mt.Gox, the bitcoin protocol was functioning normally. In recent days,Mt. Gox had stopped withdrawals, citing an alleged flaw in theprotocol.

Since at least 2011, enthusiasts have been trading bitcoins fordollars and other traditional currencies, and in early 2013 Mt. Goxwas one of the biggest exchanges. Mt. Gox said this month that itidentified a bug that enables people to withdraw the same bitcoinsmore than once, leaving it vulnerable to hackers.

Prices quoted on the exchange plunged on speculation thataccount holders wouldn't be able to get their coins back.

The troubles at Mt. Gox are the latest setback for bitcoin afterauthorities in Russia, China, and Israel sought to restrict the digital money, whilethe U.S. seeks ways to prevent money laundering and illicitsales without killing the new technology.

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