North Korean hackers were behind a sophisticated hack that stole about $1.5 billion worth of digital currency from Bybit, a major cryptocurrency exchange, according to security firm TRM.

“TRM has determined – with high confidence – that the Bybit hack was perpetrated by North Korean hackers,” a statement from the firm read Friday.

“This assessment is based on substantial overlaps observed between addresses controlled by the Bybit hackers and those linked to prior North Korean thefts,” the statement continued.

TRM said the firm was able to tag and track in real time the movement of the stolen $1.5 billion in Ethereum tokens.

The Hill has reached out to the FBI for comment.

North Korean state hackers have been linked to several high-dollar crypto thefts in recent years. In December, the FBI, the Defense Department, and the National Police Agency of Japan issued a joint statement blaming North Korean hackers for the theft of $308 million from a Japanese crypto firm.

Bybit said on Friday a routine transfer of Ethereum digital wallets was “manipulated” by an attacker who transferred the crypto to an unidentified address.

The company sought to reassure customers that their cryptocurrency holdings with the exchange were safe. The company added that news of the hack had led to a surge in withdrawal requests and there could be delays in processing them.

Bybit CEO Ben Zhou said on social media that his company would remain solvent even if the hacked crypto wasn’t recovered.

“We can cover the loss,” he said.

The Associated Press contributed.