NiceHash, a marketplace for cloud-based mining of cryptocurrencies, made its announcement following an hours-long outage attributed to "maintenance" and reports from NiceHash users that their wallets had been emptied. NiceHash paused operations for 24 hours to determine how many bitcoins were stolen and how. But a Coindesk report suggests the wallet contained 4,736 bitcoins, worth about $66 million at current prices.
"This is a matter of deep concern and we are working hard to rectify the matter in the coming days," the Slovenia-based NiceHash said in a statement. "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."
In the meantime, NiceHash is recommending users change their passwords.
Bitcoin has proved popular with currency traders, going on a massive bull run in 2017. On Jan. 1 this year, bitcoin was priced at just under $1,000. On Wednesday, the currency rose $2,170 to $14,095 before settling to $13,696 as of this writing and giving it a market capitalization of $231 billion.
This isn't the first time a bitcoin wallet has fallen victim to security shortfalls. One of the most famous security lapses resulted in bitcoin exchange Mt. Gox filing for bankruptcy in 2014 after losing nearly 850,000 customers and exchange bitcoins.