Flexcoin, a Bitcoin bank, was forced to shutdown after hackers stole 896 units of the digital currency, the Guardian newspaper reported.

Flexcoin shut its website and posted a statement March 4 detailing the loss after the March 2 theft, according to the newspaper. The company still had some Bitcoins in "cold storage," meaning they were held in devices not connected to the Internet, the Guardian said.

Flexcoin executives didn't immediately respond to requests for comment sent to e-mail addresses on the company's website.

The reported theft underscores security concerns over the virtual currency, which has no central issuing authority and uses a public ledger to verify transactions while preserving users' anonymity. Mt. Gox, once the world's largest exchange for the digital currency, filed for bankruptcy in Tokyo last week after losing 750,000 Bitcoins belonging to clients.

As Mt. Gox's operations unraveled, U.S. and Japanese prosecutors opened investigations into the company while U.S. regulators began exploring ways to increase oversight of virtual currencies. The European Banking Authority said Feb. 28 it would create a task force to review ways to regulate Bitcoinand its derivatives.

Jinyoung Lee Englund, director of public affairs of the Bitcoin Foundation, an advocacy group for the currency, didn't immediately respond to an e-mail seeking comment.

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