Japanese crypto exchange DMM Bitcoin lost 4,502.9 Bitcoin worth about $308 million in what it called an “unauthorised leak,” according to crypto security company Elliptic.
Elliptic said if hacking were to be confirmed as the cause it would amount to the eighth-biggest crypto theft in history.
DMM said it was investigating and had taken measures to prevent further outflows.
The company also said it had implemented restrictions on some services for additional safety, including crypto withdrawal processing.
It added that all Bitcoin deposits were guaranteed.
“Please rest assured that we will procure the equivalent amount of BTC leaked with support from our group companies and guarantee the full amount of the entire amount of Bitcoin deposited by our customers,” the company said in a blog post that was written in Japanese and machine translated.
Elliptic said if confirmed, it would be the biggest hack since November 2022, when now-bankrupt crypto exchange FTX suffered a $477 million exploit.
The security company added that its investigative tools had determined the Bitcoin from DMM had been split and sent to new wallets.
According to a crime report by blockchain analysis company Chainalysis, about $1.7 billion in crypto was stolen last year, down from $3.7 billion in 2022.