More details have emerged into what led MtGox, one of the largest Bitcoin exchanges, to file for bankruptcy.
There was a "high probability" that the bitcoins had been stolen through a bug in MtGox's systems, the firm said in a statement.
Investigations to find the culprits are under way, it added.
MtGox filed for bankruptcy in Japan on Friday. Days earlier the site had closed down after losing an estimated 750,000 of its customers' bitcoins.
Much of the statement released on MtGox's website confirmed details contained in a leaked document that surfaced just days before the bankruptcy application.
As well as the 750,000 bitcoins belonging to customers that were lost, the company said it had also lost approximately 100,000 of its own. This amounts to nearly $500m (£300m).
It also said MtGox accounts held with financial institutions currently contained approximately 2.8bn yen (£16.5m) less than the amount MtGox users had deposited.
To "establish the truth" about what had happened a "huge amount of transaction reports" would need to be investigated, MtGox said.
Because of this, MtGox could not give an exact amount of missing deposit funds or the total amount of bitcoins that had disappeared.
MtGox also said that it had appointed an expert to look at the possibility of criminal proceedings.
"We will make all efforts to ensure that crimes are punished and damages are recovered," it said.
The possibility of continuing as a business in order to pay back creditors was also being explored, the company said.
A call centre has also been set up to answer customers questions.
Japan said on Tuesday that the government was still trying to determine what had led to the collapse of MtGox.
"We still have not had a clear grasp of the situation," Japanese Finance Minister Taro Aso said, according to Reuters.
"[We] don't know if it was a crime or just a bankruptcy."
Meanwhile another Bitcoin bank - Flexcoin - has announced that it too is going out of business, following a hack attack which saw 896 coins stolen. It is working with law enforcement to trace the source of the hack.
"As Flexcoin does not have the resources, assets, or otherwise to come back from this loss, we are closing our doors immediately," it said.
The European Banking Authority (EBA) is set to create a taskforce to advise on whether virtual currencies should be regulated.
The watchdog, which is due to be created before July, will analyse the risk to consumers of using virtual currencies such as bitcoins.