DMM, a Japan-based cryptocurrency exchange, confirmed a cyberattack resulting in the theft of 4,502.9 BTC, valued at about 48 billion yen ($305 million). The exchange detected an unauthorized Bitcoin transfer from its wallet at approximately 1:26 pm Tokyo time on Friday, May 31, 2024, according to a statement released on that date.

Elliptic, a blockchain analytics firm, identified this incident as the eighth-largest crypto theft in history and the largest since FTX exchange's collapse in November 2022, when $477 million was stolen.

In response to the breach, DMM swiftly halted cryptocurrency withdrawals and restricted spot-buying activities to mitigate further losses. It also cautioned users about potential delays in withdrawing Japanese yen.

DMM assured affected customers that all stolen Bitcoin deposits would be fully reimbursed, though specific timelines for reimbursement were not provided. The exchange pledged:

"All Bitcoin (BTC) deposits will be fully guaranteed, as we will procure the equivalent amount of BTC that was stolen with support from our group companies."

DMM did not specify when its services would resume but promised to update users through a subsequent announcement.

Speculation within the cryptocurrency community suggested that the breach might have compromised all customer BTC holdings, impacting both hot and cold wallets. However, the complete scope of the breach remained unclear at the time of reporting. According to local regulations, DMM is required to store at least 95% of customer crypto assets in cold wallets.

This incident ranks among Japan's largest cryptocurrency exchange hacks. Previously, in 2018, Coincheck suffered a theft of 58 billion yen ($533 million) in crypto, and in 2014, the now-defunct Mt. Gox exchange lost over 140,000 BTC belonging to its customers.