A Binance software engineer who thought he was interviewing for a new job downloaded a coding assignment that gave hackers access to his work computer, the cryptocurrency exchange said Tuesday in a detailed account of how attackers stole a record $6.3 billion from its digital wallets last week.

The FBI attributed the Oct. 29 theft to North Korea over the weekend. The bureau has asked cryptocurrency firms to block transactions involving the stolen funds. The DPRK has denied involvement, South Korean news agency Yonhap reported Monday, citing state media. 

Binance traced the campaign back to June, when a member of its team downloaded a tampered software installer while trying to set up an AI coding tool. 

The company caught the intrusion,…