LuBian

On December 28, 2020, roughly 127,000 BTC — worth about $3.5 billion at the time — drained out of wallets controlled by LuBian, a Chinese-Iranian bitcoin mining pool that briefly ranked among the world's top ten and controlled close to 6% of global hashrate. The loss went unreported. LuBian quietly stopped operating within weeks, and the theft stayed hidden until blockchain analytics firm Arkham Intelligence traced it in August 2025, nearly five years later.

How the attack worked

This wasn't phishing, a compromised admin account, or a smart-contract bug — there was no smart contract involved at all. Arkham's analysis points to a flaw in how LuBian's wallet software generated private keys: instead of drawing on a properly random seed, the algorithm produced keys from a much smaller, predictable space of possible values. That turns a task that should be computationally impossible — guessing a 256-bit private key — into a brute-force search over a manageable set of candidates. Whoever found the flaw didn't need to breach a server or trick an employee; they only needed to run the same weak algorithm forward until it produced a match. Over 90% of the pool's holdings were swept out in a single day, with a smaller follow-up transfer of BTC and Omni-layer USDT two days later.

What happened next

LuBian tried to negotiate: on-chain records show the pool sent well over a thousand small transactions to the attacker's wallets carrying a plea to return the funds for a reward, spending roughly $40,000 worth of BTC on the messages alone (Bitcoin News). There was no reply, and the pool had shut down by February 2021. The stolen coins then sat untouched for years until Arkham observed the wallets moving again in 2024. That led to a second, more consequential twist: in October 2025 the US Department of Justice unsealed the largest civil forfeiture in its history, seizing roughly 127,271 BTC — by then worth about $15 billion — from wallets prosecutors linked to Chen Zhi, chairman of Cambodia's Prince Group. According to the indictment and Elliptic's analysis, LuBian itself operated as a mining front used to launder proceeds from Prince Group's forced-labor scam compounds. That leaves an open question neither firm fully answers: whether an outside party actually stole the coins, or whether the "theft" was an internal transfer inside Chen Zhi's own network. Either way, none of the $3.5 billion has been returned to LuBian or to anyone claiming to be a victim — the coins are now forfeited to the US government as proceeds of an unrelated fraud case.

What this means

• Mining pools custody balances as large as exchanges do, but without comparable security audits or disclosure obligations — a flaw in key-generation code can sit undetected for years because nothing forces the operator to admit a loss.
• Key length is meaningless if the generation process isn't truly random. A "brute-forceable" 256-bit key almost always means the randomness source was broken, not that raw computing power caught up with the math — the same bug class has hit other bitcoin wallets with flawed entropy.
• Depositors in a custodial pool or wallet have no visible signal that key generation is weak; the closest practical safeguard is favoring providers that document their key-generation method and have it independently reviewed.
• Bitcoin's public ledger cuts both ways: it let this loss stay invisible for five years, but the same permanence let analysts trace the coins the moment they moved again — traceability that ultimately fed a law-enforcement seizure, not a recovery for anyone harmed by the original loss.