Nearly $64 million in bitcoin has been stolen following a hack that affected “bitcoin mining marketplace” NiceHash.

NiceHash announced the breach in a statement on Wednesday, where they recommended that users change their passwords.

“Unfortunately, there has been a security breach involving NiceHash website. We are currently investigating the nature of the incident and, as a result, we are stopping all operations for the next 24 hours,” the company declared. “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.”

“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,” NiceHash explained, adding, “We are fully committed to restoring the NiceHash service with the highest security measures at the earliest opportunity.”

We would not exist without our devoted buyers and miners all around the globe. 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. While the full scope of what happened is not yet known, we recommend, as a precaution, that you change your online passwords. We are truly sorry for any inconvenience that this may have caused and are committing every resource towards solving this issue as soon as possible.

The number of bitcoin stolen has since been revealed: approximately 4,700 bitcoins, or roughly $63.92 million dollars as of this writing. Bitcoin’s value has been changing so rapidly in recent days that even Breitbart News’ article explaining the $10,000 value milestone last week is now lagging far behind the digital currency’s value.

NiceHash’s Head of Marketing, Andrej P Škraba claimed that the hack was “a highly professional attack with sophisticated social engineering.”

According to the Guardian, “NiceHash is a digital currency marketplace that matches people looking to sell processing time on their computers for so-called miners to verify bitcoin users’ transactions in exchange for the bitcoin.”

Several users of the service complained online following the hack, accosting NiceHash for keeping so much bitcoin in a single wallet.

“In hindsight, NH shouldn’t have kept so much money in a single online wallet,” posted one user on Reddit. “They should have spread on multiple offline wallets in different physical locations to mitigate damage.”

Charlie Nash is a reporter for Breitbart Tech. You can follow him on Twitter @MrNashington and Gab @Nash, or like his page at Facebook.