The alleged victim, @83_5BTC, revealed that after transferring 139 BTC to a new cold wallet, the funds were immediately swept to another wallet by the attackers. The transaction split the sum, sending 55.77 BTC to the hackers’ wallet, while the rest, a staggering 83.65 BTC, was paid as a transaction fee. This incident surpasses the previous high-fee record of 19.8 BTC.
Mononaut, the anonymous operator behind the mempool.space bitcoin explorer, weighed in on the incident. He suggested that “the most likely explanation is that the wallet was generated from bad entropy.” In layman’s terms, this means the wallet’s security was compromised due to weak randomization in its creation process. Mononaut’s insight provides a crucial understanding of the technical flaw that may have led to this unfortunate event.
source This is the classic example on how everyone should manage their wallet if they have huge amount on it. Perhaps he should used multi-sig, 2 out of 3 and it increases the security, requiring at least 2 co signers.
Unless, the hackers also got the other keys, which could be very difficult unless it's a physical attack or the 5 dollar wrench attack.