The website of Tokyo-based bitcoin exchange MtGox went down 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 several 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 on Tuesday afternoon.
It was not immediately possible to verify the document.
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.
A joint statement issued by CEOs of major platforms said the currency was sound and blamed MtGox for the fiasco.
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 complex 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.
Proponents say the currency is an efficient and anonymous way to store and transfer monetary value and to avoid the risks inherent in any currency dependent on the viability of a government for its value.
But some economists say the project is mired in difficulties, including large fluctuations in value caused by speculators and a supposed vulnerability to online thieves.
Others note that the anonymity it offers is attractive to underworld figures and cite its use to buy drugs and guns on the underground Silk Road website.
MtGox has not responded to repeated requests from AFP for comment, but in a statement last week said it was still working on "re-initiating bitcoin withdrawals".
On the eve of service shutdown, MtGox CEO Mark Karpeles resigned from the board of the Bitcoin Foundation, which is an advocate for the virtual currency.
A handful of MtGox clients have staged small protests outside the firm's headquarters, but say they have not received any reassurances over whether or not their money is safe.
