Tokyo Bitcoin exchange website disappears amid robbery claims

The website of Tokyo-based Bitcoin exchange MtGox went down Tuesday amid reports of a theft of the virtual currency worth hundreds of millions of dollars, dealing a blow to its credibility.

The Bitcoin community rallied round to defend the unit, with chief executives of major operators pledging to work together to shore up public faith in the project.

Visitors to the www.mtgox.com domain on Tuesday got a blank page - consistent with contents having been removed - when they tried to log on, more than two weeks after the firm suspended cash withdrawals and claimed there was a bug in the software underpinning the crypto-currency.

A widely shared document purporting to be a MtGox "crisis strategy" said the firm might have lost more than 744,400 Bitcoins in a theft that had gone unnoticed for years.

That number of Bitcoins would be worth more than $300 million, using rates at functioning exchanges Tuesday afternoon.

It was not immediately possible to verify the document, posted on a blog written by someone who describes himself as "an entrepreneur and former VC who makes the business case for #Bitcoin".

Consternation has grown since MtGox stopped processing external transactions on February 7, claiming there was a problem with the program that powers the currency and allows it to be transferred between users or swapped for goods and services.

The value of the unit on MtGox had gone into freefall since then. Around midday on Tuesday shortly before the shutdown, a Bitcoin was worth $135 compared with the $430 quoted by the CoinDesk Bitcoin price index, which tracks the price of the currency on major exchanges.

Prices among exchanges are not always the same.

In January a Bitcoin was worth more than $900 at MtGox, one of the world's first exchanges for the unit.

A joint statement issued by CEOs of major platforms said the currency was sound and blamed MtGox for the fiasco.

"This tragic violation of the trust of users of MtGox was the result of one company's actions and does not reflect the resilience or value of Bitcoin and the digital currency industry," said the statement from Coinbase, Kraken, bitstamp.net, BTC China, blockchain.info and Circle.

"As with any new industry, there are certain bad actors that need to be weeded out, and that is what we are seeing today. MtGox has confirmed its issues in private discussions with other members of the Bitcoin community," it said.

Wild volatility has long been a part of the experimental digital currency, which does not have backing of a central bank or government and falls outside of traditional financial regulatory frameworks.

Units are generated by a computer algorithm designed by one or more anonymous people in 2009, with a global cap on the eventual number of Bitcoins set at 21 million units.