The announcement came after hours of speculation sparked by the service being unavailable for the better part of Wednesday.
A wallet address circulated by NiceHash users shows that more than US$60m of bitcoins might be affected, according to CoinDesk, the cryptocurrency research and news website. While the company did not reveal the exact amount lost, users on Reddit spent the better part of today anxious as the service was initially "under maintenance" for 12 hours amidst suspicious transactions on the blockchain that saw 4,736.42 BTC taken from Nicehash and their Nicehash internal wallets reporting zero balances. The company also apologized to its users for "any inconvenience" the breach may have caused.
Andrej Skraba, NiceHash's head of marketing, told Reuters about 4,700 bitcoin were lost, which is worth about $66m at current prices.
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Mr Copson was described by the whistle-blower as responding, "I couldn't be better", and that he was "going to celebrate today". Cummings did not name the whistleblower in the letter, but offered to have Gowdy speak with the person directly.
"Unfortunately, there has been a security breach involving NiceHash website", the company wrote, adding that it was freezing all operations for at least the next 24 hours while it investigated the hack.
The statement said, "Clearly, this is a matter of deep concern and we are working hard to rectify the matter in the coming days".
"The incident has been reported to the relevant authorities and law enforcement and we are cooperating with them as a matter of urgency", it said. The amounts mined are held in trust by NiceHash with the company naturally taking its own cut of the transaction with users then being able to transfer bitcoin or other cryptocurrencies earned via the service to their own wallets.
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While the full scope of what happened is not yet known, we recommend, as a precaution, that you change your online passwords.