DMM, the cryptocurrency arm of Japanese internet giant DMM.com, announced on Friday that more than $300 million worth of bitcoins had been stolen in a major security breach.

The exchange confirmed the incident but did not explain how the assets were stolen. DMM Bitcoin suddenly froze most of its services, including deposits, withdrawals and trading of almost all cryptocurrencies.

“At approximately 1:26 p.m. on Friday, May 31, 2024, we detected an unauthorized bitcoin leak from our wallet,” DMM Bitcoin stated. The announcement, originally in Japanese, was translated into English and posted on the company’s website.

The exchange said 4,502.9 bitcoins worth approximately $306 million were seized in the breach. DMM Bitcoin has assured its customers that their Bitcoin deposits will be fully refunded. “Please rest assured that all your Bitcoin deposits will be fully guaranteed as we will acquire the equivalent of the BTC that was leaked with the support of our group companies,” the statement reads.

In a blog post on its website, DMM Bitcoin reiterated that measures have been taken to prevent further unauthorized outflows of funds. The exchange restricted all spot purchases on the platform and warned that Japanese yen withdrawals may take longer than usual due to the incident.

In 2018, rival exchange Coincheck experienced one of the largest hacking attacks in the history of the industry, resulting in the loss of approximately $534 million (XEM) from its balmy wallet. During this time, the Monex Group subsidiary spent several weeks trying to identify the attackers and understand how the breach occurred.

The Coincheck hack had widespread consequences for both the company and the broader Japanese cryptocurrency industry. Moreover, his reputation was seriously damaged as a result of the hack. In addition to financial losses, the company faced widespread criticism for inadequate security measures and failure to safeguard user funds.