North Korean hackers were responsible for stealing $625 million in cryptocurrency from Ronin Network, an Ethereum-linked sidechain that supports the popular blockchain-based video game Axie Infinity.

Last month, Ronin Network disclosed that hackers stole 173,600 Ethereum and 25.2 million USDC stablecoins. Sky Mavis is the developer of Axie Infinity and the operator of the Ronin Network.

The Federal Bureau of Investigation (FBI) confirmed that the Lazarus Group and the Advanced Persistent Threat 38  (APT38) were behind the cryptocurrency theft. These hacking groups are known as the military hacking units of the Democratic People's Republic of Korea (DPRK), the official name of  North Korea.

"Through our investigation, we were able to confirm Lazarus Group and APT38, cyber actors associated with the DPRK,  are responsible for the theft of $620 million in Ethereum reported on March 29. The FBI, in coordination with Treasury and other U.S. government partners, will continue to expose and combat the DPRK’s use of illicit activities – including cybercrime and cryptocurrency theft – to generate revenue for the regime," according to the bureau in a statement.

On the other hand, the Vietnam-based video game developer expressed gratitude to all law enforcement agencies that supported its ongoing investigation into the hacking of Ronin Network.

The company also stated that the U.S. Treasury Department "sanctioned the address that received the stolen funds." It is also adding security measures before redeploying the Ronin Bridge to prevent future risk.

The cyberattack on the Ronin Network is one of the largest cryptocurrency theft to date.

The Lazarus Group was behind some of the high-profile cyberattacks including the hacking of the computer systems of Sony Pictures in 2014.  This group was also responsible for the WannaCry ransomware attacks that affected around 230,999 computer networks globally.

Last year, the United States government filed criminal charges against three North Korean hackers for participating in damaging cyber attacks The defendants identified as Jon Chang Hyok (전창혁), Kim Il (김일), and Park Jin Hyok (박진혁) were allegedly involved in the theft and extortion of more than $1.3 billion in cash and cryptocurrency from companies and financial institutions.

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