Prominent Bitcoin mining pool reported losing $3 million worth of digital assets in a cyber-attack carried out earlier this month.

In a press release on Monday, NYSE-listed BIT Mining said that its subsidiary experienced a cyber-attack on Dec. 3. Hackers stole digital assets worth $700,000 from’s clients and $2.3 million from the company.

The firm said it had alerted local law enforcement authorities in Shenzhen, China and an official investigation commenced on Dec. 23. BIT Mining said it has already secured some of’s digital assets as a result of this coordination with authorities.

“ is currently operating its business as usual, and apart from its digital asset services, its client fund services are unaffected,” read the announcement. is the seventh-largest mining pool accounting for 630874.3861 peta hashes per second, which amounts to 2.5% of Bitcoin’s total hash rate. Its parent company BIT Mining’s shares declined 17% on Monday and are down 97% year-to-date.

Crypto mining companies have had a rough year plagued by an increasing mining difficulty and a declining Bitcoin price. According to data from Y Charts, Bitcoin mining difficulty hit an all-time high of 36.95 trillion hashes on Dec. 4. The increase in difficulty typically occurs when a large number of participants are attempting to mine Bitcoin, implying a higher degree of competition in the market.

The heightened competition, coupled with mostly negative price action from Bitcoin itself has led most miners to a dire situation of high capital expenditure with little to no profits. Last week, major Bitcoin miner Core Scientific filed for Chapter 11 bankruptcy, reporting a $650 million loss over a 3-month period.