On Wednesday evening, Bitfloor, the number four Bitcoin-based exchange (behind Mt. Gox, BTC-E, and Bitstamp) announced that it is closing its doors “indefinitely.”

“Unfortunately, our US bank account is scheduled to be closed and we can no longer provide the same level of [US dollar] deposits and withdrawals as we have in the past,” wrote Roman Shtylman, the exchange’s founder. “As such, I have made the decision to halt operations and return all funds. Over the next days we will be working with all clients to ensure that everyone receives their funds. Please be patient as we process your request.”

Ars reached out to Shtylman to find out more details, but he did not immediately respond.

When the world’s biggest Bitcoin exchange, Mt. Gox, suspended trading last week, Bitfloor provided one of the few alternative means of trading bitcoins online.

Bitfloor had seen problems of its own, however. Last year, the site lost 25,000 bitcoins when its trading server was compromised by unknown hackers. Collectively, those bitcoins would be worth over $2 million at present-day exchange rates.