North Korean-tied hackers were responsible for a $620m cryptocurrency heist last month targeting players of the popular Axie Infinity game, US authorities said Thursday. The hack was one of the biggest to hit the crypto world, raising huge questions about security in an industry that only recently burst into the mainstream thanks to celebrity promotions and promises of untold wealth. Last month’s theft from the makers of Axie Infinity, a game where players can earn crypto through game play or trading their avatars, came just weeks after thieves made off with around $320m in a similar attack. “Through our investigations we were able to confirm Lazarus Group and APT38, cyber actors associated with (North Korea), are responsible for the theft,” the FBI said in a statement. Lazarus Group gained notoriety in 2014 when it was accused of hacking into Sony Pictures Entertainment as revenge for “The Interview,” a satirical film that mocked North Korean leader Kim Jong Un. North Korea’s cyber-program dates back to at least the mid-1990s but has since grown to a 6,000-strong cyber warfare unit, known as Bureau 121, that operates from several countries including Belarus, China, India, Malaysia and Russia, according to a 2020 US military report. North Korean hackers stole around $400m worth of cryptocurrency through cyber-attacks on digital currency outlets last year, blockchain data platform Chainalysis said in January.