Chainalysis said the hackers are deliberately keeping the funds idle to avoid heightened scrutiny after the high-profile incident.

Researchers spot the stolen funds moving through cryptocurrency wallets that were used in earlier heists attributed to North Korea's Lazarus hacking group.

Cryptocurrency exchange Bybit said last week hackers had stolen digital tokens worth around $1.5 billion, in what researchers called the biggest crypto heist of all time. Bybit CEO Ben Zhou said the crypto was taken from a "cold wallet" - a digital wallet usually stored offline and so supposedly more secure - that was used for ether tokens.