In a shocking revelation, blockchain analytics firm Arkham Intelligence has uncovered a record-breaking $3.5 billion Bitcoin hack that took place in 2020, and went unnoticed until now. The target was Chinese mining pool LuBian, which ranked as the sixth-largest Bitcoin mining pool at the time.

According to Arkham, hackers struck on December 28, 2020, stealing 127,426 BTC — nearly 90% of LuBian’s holdings. Only 11,886 BTC was salvaged and transferred to safer wallets. No public announcement was ever made, and the heist remained hidden for nearly four years.

Arkham revealed that LuBian left clues in the form of 1,516 OP_RETURN messages on the Bitcoin blockchain, tagging the hacker’s wallets. This cost the pool about 1.4 BTC. Investigators believe the breach may have stemmed from weak private key generation vulnerable to brute-force attacks — a fatal security oversight.

At today’s market value, the stolen Bitcoin is worth over $14.5 billion, making it the largest crypto hack in history, surpassing the previously reported $1.5 billion ByBit hack in February 2025. That breach was linked to a compromised developer machine used to access sensitive infrastructure via AWS tokens without detection.

Another major attack in April 2025 saw an elderly investor lose $330 million in BTC to a sophisticated social engineering scam. Only $7 million was recovered.

These incidents serve as critical reminders of the importance of private key security, safe wallet infrastructure, and the dangers of social engineering in crypto. As hacks grow in scale and stealth, security protocols must evolve just as fast.