North Korean hackers were likely behind the theft of at least $35 million from a popular cryptocurrency service, multiple crypto-tracking experts told CNN Tuesday.

It’s the latest in a string of hacks of cryptocurrency firms linked to Pyongyang that US officials worry could be used to fund the North Korean regime’s nuclear and ballistic weapons programs.

The hackers drained the cryptocurrency accounts of certain customers of Atomic Wallet, an Estonia-based company that claims 5 million users of its software.

Atomic Wallet said on Saturday that “less than 1%” of monthly users appeared to be affected by the hack. The firm has not specified how much money might have been stolen or who was behind the hack. CNN has requested comment from the firm.

Some of the apparent victims of the hack took to Twitter to beg the hackers for their money back, posting their cryptocurrency addresses in case the hackers took pity on them.

North Korean hackers have stolen billions of dollars from banks and cryptocurrency firms over the last several years, providing a key source of revenue for the regime, according to reports from the United Nations and private firms.

In the Atomic Wallet incident, the hackers’ money-laundering techniques and the tools they used matched telltale North Korean behavior, according to London-based crypto-tracking firm Elliptic.

An independent cryptocurrency tracker known as ZachXBT told CNN that North Korean hackers were very likely responsible. The amount confirmed stolen could rise above $35 million as Atomic Wallet continues to investigate the incident, the analyst said.

“The pattern was similar to what we saw with the laundering of Harmony funds back in January,” ZachXBT said, referring to the laundering of $100 million stolen from a California-based firm.

The FBI blamed North Korea for the hack of Harmony. CNN reported on how private investigators and South Korean intelligence operatives were able to claw back a fraction of that money.

Thwarting North Korean hacking and money laundering has quickly become a national security priority for the Biden administration. About half of North Korea’s missile program has been funded by cyberattacks and cryptocurrency theft, a White House official said last month.

CNN has requested comment from the FBI on the Atomic Wallet hack.

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