Millions of dollars worth of bitcoin are potentially missing after a security breach at cryptocurrency mining marketplace NiceHash.
In a post on its Facebook page late last night, NiceHash said it was investigating the nature of the incident and would stop all operations for 24 hours.
"Importantly, our payment system was compromised and the contents of the NiceHash bitcoin wallet have been stolen. We are working to verify the precise number of BTC taken," the company said.
Andrej Skraba, NiceHash's head of marketing, told Reuters about 4,700 bitcoin were lost, which is worth about $66m (£49m) at current prices.
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"Clearly, this is a matter of deep concern and we are working hard to rectify the matter in the coming days. In addition to undertaking our own investigation, the incident has been reported to the relevant authorities and law enforcement and we are co-operating with them as a matter of urgency," it said.
NiceHash advised users to change their online passwords.
"We understand that you will have a lot of questions, and we ask for patience and understanding while we investigate the causes and find the appropriate solutions for the future of the service. We will endeavour to update you at regular intervals."
NiceHash is a marketplace that allows customers to trade cryptocurrency mining power for bitcoin.
Hacks aren't the only way to lose bitcoin though - last week it emerged that Welsh IT worker James Howells, an early bitcoin investor, threw out his old computer that had the ownership codes to 7,500 bitcoins.