Bitcoin thieves yet to spend stolen hoard

People keep bitcoins at an exchange so they can easily swap them for "real" currencies

Cyberthieves who stole more than $250,000 (£158,000) in digital money are still sitting on the cash.

The haul, in what is known as bitcoins, was stolen in a raid on the Bitfloor online currency exchange this month.

Bitfloor boss Roman Shtylman said transaction-tracking technology in the bitcoin system showed the money had not been spent.

The robbery forced Bitfloor to close but Mr Shtylman said he was working on ways to relaunch the exchange.

Crime report

Although bitcoins can be used to buy and sell, the digital currency is not minted by a nation. Instead bitcoins are "mined" by people getting their computer to perform a complicated and time-consuming mathematical problem.

Bitcoins are spent by assigning the private key associated with them to someone else. The robbery on Bitfloor got hold of the private keys of many of the exchange's customers, thereby handing control of those bitcoins to the robbers.

Because all transactions with bitcoins are public, said Mr Shtylman, everyone who used the coins knew that the thieves had yet to start spending their ill-gotten gains.

Digital detective work carried out soon after the theft showed that it was carried out via an IP address based in Moscow, he said. No transactions had been recorded using the stolen coins since they had been taken.

"They have not been moved," Mr Shtylman told the BBC. "We may not know who the person is but we can see what they are doing with the fund."

He speculated that the thieves were sitting on their pile of digital cash because the money was still "hot". The thieves may be looking at ways to launder the money, he said, by putting it into bitcoin wallets they controlled and then converting it into other, real-world, currencies.

Mr Shtylman said a crime report about the theft had been filed with the FBI, which was believed to be investigating.

Prior to the raid Bitfloor was the largest bitcoin exchange in America and the fourth-largest in the world. Mr Shtylman said he was now looking at how best to relaunch Bitfloor.

"Given the amount of money involved it will take time to solve these problems and find ways to pay people back," he said, adding that most of the currency traders who used Bitfloor were sticking with him.

"A lot of people want to see the exchange return and continue trading," he said.