Binance said hackers used fake job interviews and a compromised internal artificial intelligence tool to breach its systems and drain $6.3 billion in cryptocurrency.

An engineer was instructed to download malware disguised as an “assignment” during a second interview, and the code used obfuscation techniques to evade detection. The agencies investigating the case said the hack bore the signs of having been orchestrated by North Korea, and Pyongyang denied on Tuesday that it was behind the theft. The exchange froze $2.85 billion in assets and replenished about 98% of the affected tokens with company funds.