The dominant cryptocurrency marketplace charged users duplicative fees for previous purchases on Thursday, emptying and over-drafting users' bank accounts.

Users of Coinbase, a digital exchange and wallet that allows people to buy, sell and store the most popular cryptocurrencies, reported being charged fees multiple times over for old transactions.

Coinbase features one of the simplest interfaces among cryptocurrency exchanges, making it a popular choice for new cryptocurrency purchasers.

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Coinbase said it was aware of the issue and that employees “are working as quickly as possible to help anyone affected by this." The company did not specify whether the issue was a technical glitch or a deliberate attack.

"We can confirm that the unexpected charges are originating outside of our control, and are related to charges from previous purchases," Coinbase said.

"To the best of our knowledge, these unexpected charges are not permanent and are in the process of being refunded. We are running joint investigations with all parties involved, and will provide updates as we receive them."

Dozens of Coinbase users with debit card and bank accounts linked to the website complained in online forums Thursday about the duplicative charges. Customers reported being charged anywhere from two to 17 times for fees they already paid.

“You drained my bank account and now I have nothing,” wrote one user on the forum’s CoinBase subsection. “I try not to overreact. But when you drain my account, MINUTES after I receive my paycheque I can't help but lose it. Please help me I have no funds anywhere now.”

“Coinbase drained my bank account,” another user wrote. “Took 5x the amount I authorized from debit. I am now broke, cannot afford rent, food, gas, bills."