In a post on the Bitcoin Forum, the exchange's founder Roman Shtylman has confirmed that approximately 24,000 coins have been stolen after intruders "gained accesses to an unencrypted backup of the wallet keys" and used them to transfer the money.

Shtylman says that he hopes to keep Bitfloor -the fourth largest bitcoin exchange - running but says that as a last resort he may have to cease operations.

If this happens, he promises to "initiate account repayment using current available funds. I still have all of the logs for accounts, trades, transfers. I know exactly how much each user currently has in their account for both USD and BTC. No records were lost in this attack."

Shtylman's post has developed into a huge thread, with concerned Bitfloor users trying to ascertain whether they wil see their money again and many expressing anger at the exchange's shoddy security.

In a separate thread, the exchange founder has posted the IP address from which the attack was initiated in a bid to enlist help in tracing the stolen coins.

The attack is the latest in a series of security-related setbacks for bitcoin: over the summer, the Bitcoinica exchange said that it was hacked and is now being sued by four former users who allege they are owed nearly half a million dollars-worth of the virtual currency, plus damages.

Last year the value of the currency plummeted after an account at MT. Gox was compromised and a large amount of coins sold off. And earlier this year, e-wallet provider Paxum ceased all business involving the virtual currency after coming under pressure from MasterCard and banks, and another major exchange, TradeHill, shut down.