A major Bitcoin currency exchange, BitFloor, has been shut down following an online ‘heist’ that saw 24,000 units of virtual currency, worth around $250,000, stolen from its servers.

BitCoins, as the currency is known, are used in online transactions and trades and in large part by speculators trading also for real money. BitCoins themselves are essentially just a secret number, associated with a 34-character alphanumeric “address” held by users and listed in a transactional basis in a publicly available log.

New York-based BitFloor acts as a virtual currency exchange platform, where account holders can buy and sell BitCoins, exchanging them for US dollars, which can then be transferred to a bank or Paypal account.

Cnet reported that the ‘virtual heist’ occurred sometime last night, after hackers managed to access an unencrypted backup of BitFloor’s keys, then helped themselves to 24,000 BTC, which represents virtually all of the exchange’s currency reserves.

But it wasn’t that the hackers found a flaw in BitFloor’s built-in security. Instead, Roman Shtylman, founder of BitFloor, admitted that he made one almighty cock-up, creating an unencrypted copy of BitFloor’s keys after upgrading the exchange’s servers.

Shtylman later owned up to his schoolboy error on a forum, saying that the backup was made following a manual upgrade. After copying the keys, he accidently left them in an unencrypted area on disk.

Now, it looks as if the very existence of BitFloor is in the balance, as Shtylman admits that he currently doesn’t possess the funds to honor all of the accounts held with his exchange.

“I realise this is a very serious mistake,” wrote Shtylman.

“As a last resort, I will be forced to fully shut BitFloor down and initiate account repayment using current available funds.”

This isn’t the first time that the security of BitCoin exchanges has come into question. UK-based BitCoinica has fallen victim to online thieves not just once, but twice in the first six months of this year, while just last month the Australian anti-money laundering watchdog AUSTRAC announced that it had assigned a higher priority of concern to BitCoins, citing fears that the currency could be used by criminals to launder the proceeds of crime.