Mixin Network: The $200M Cloud Heist

In the early hours of 23 September 2023, Hong Kong time, someone got into a database run by the company that hosted Mixin Network's computers. By the time Mixin's founder, Feng Xiaodong, went on a livestream two days later, about $200 million in customers' crypto had gone. Nobody broke Mixin's code. The thieves came in through the landlord.

Mixin was a Hong Kong based wallet and payments service: an app where people kept bitcoin, ether and digital dollars and sent them to each other instantly, much as a brokerage app holds shares on a client's behalf. It described itself as a "free, lightning-fast and decentralized network". The keys that controlled the money, the digital equivalent of a bank's vault combination, depended on a database held by an outside cloud company. Mixin has not publicly named that company.

The haul, as tracked on the public blockchains, was about 59,854 ether, 891 bitcoin and roughly $23.57 million in USDT, a stablecoin, which is a crypto token designed to stay worth exactly one dollar. Mixin's own headline figure was $200 million. Merkle Science, a blockchain analytics firm, added up what the thieves' wallets actually received and reached about $144 million at the prices of the day; Mixin's own help pages later put the damage at about $150 million. The gap is mostly a matter of what was counted and at which prices; nobody disputes that it was one of the biggest thefts of 2023.

How the money left

Merkle Science counted more than 11,400 separate Mixin ether wallets and 127 bitcoin wallets emptied into a handful of addresses, in more than 10,000 transactions. That pattern matters. A thief who steals one master password empties one account. A thief who can read the vault combinations for thousands of accounts at once empties them all, one after another, which is what happened here.

The stolen USDT was swapped within hours into DAI, a different dollar token. The reason is simple: Tether, the company behind USDT, can freeze tokens on request, the way a bank can freeze an account. DAI is run by software rather than a company, and nobody can freeze it on a victim's behalf. The ether and bitcoin were simply left where they landed.

Mixin suspended deposits and withdrawals, said it had called in Google's security team and the blockchain security firm SlowMist, and on 25 September Feng told viewers of his Mandarin livestream that the company could "only ensure at least half of the assets are secure". XIN, Mixin's own token, which trades a little like a share in the business, fell about 8% to around $195 that day, according to CoinGecko data cited by The Block.

Two days later Mixin wrote directly to the thieves, in a message attached to a blockchain transaction, the only address it had for them. "Most of our platform assets were users," it said, asking for the money back and offering them $20 million of it to keep as a "bug bounty", the reward normally paid to people who report security flaws. The blockchain security firm PeckShield spotted the message. Nobody replied.

Who paid for it

Mixin did not have $150 million spare. Instead it turned part of every affected balance into IOUs. When customers moved to Mixin's rebuilt system, a fixed share of each holding was swapped for a Mixin Debt Token, or MDT, a promise to pay a set number of dollars later, much like a company handing creditors bonds instead of cash. According to Mixin's own help pages, 90% of each customer's USDT on the Ethereum network became MDTu, 70% of their ether became MDTe, and 10% of their bitcoin became MDTb. The rest stayed in the customer's wallet.

The detail that stings is the price. The debt was fixed in dollars at 23 September 2023 prices: $1,592 an ether and $26,569 a bitcoin. One ether lost became 1,114.40 dollars of MDTe, and stays that. Customers who had held crypto, not dollars, lost the rise in its value as well as the coins.

Mixin promised to buy back the debt tokens out of future profits, repaying in strict order: MDTu first, then MDTe, then MDTb. It also promised that if the thief ever returned the stolen coins, holders could swap their debt tokens for the original assets. In 2024 it offered a way out for anyone who did not want to wait: a one-way swap of debt tokens into MAO, the token of the Mixin Autonomous Organization, a fund steered by votes of XIN holders, at about 6,000 MAO for each MDT.

The model is an old one. When the exchange Bitfinex was robbed in 2016, it cut every customer's balance and issued BFX tokens for the shortfall, then bought them all back within eight months. Mixin's repayment has been far slower.

Three years later

In October 2025 Mixin set itself a deadline: the roughly $23 million owed through MDTu would be repaid in full by 23 September 2026, three years to the day after the breach. On that date Mixin announced it had done so, according to the Chinese crypto outlet TechFlow, whose report was republished by KuCoin's news service. "Trust is built through commitments," Mixin said, "and maintained through concrete actions and final outcomes." Mixin's own help pages, updated in early October 2026, still describe the September deadline as a plan and have not posted a separate completion notice.

MDTu was the smallest of the three debts. Mixin's announcement says there is still no confirmed repayment schedule for MDTe or MDTb, the debts owed to the people who lost ether and bitcoin, which together covered most of the money taken. Mixin says it will set one when "conditions allow".

The thief, meanwhile, has done almost nothing. For more than two years the stolen coins did not move at all, the usual tactic of waiting until investigators stop watching. On 12 February 2026 a wallet tagged by Arkham Intelligence as the "Mixin Hacker" sent 2,005 ether, about $3.85 million, to a fresh address that pushed it straight into Tornado Cash in 20 transactions. Tornado Cash is a mixer: it pools many people's coins together so that what comes out cannot be matched to what went in, like dropping banknotes into a giant shared pot and taking out different ones. Soon after, three newly created wallets drew 2,087 ether from the mixer and sold it at about $1,933 each, according to Lookonchain, an on-chain tracking account.

According to Arkham's figures, cited by The Block, the hacker's wallets still held 57,849 ether and all 891 bitcoin after that move, worth about $173 million together in February 2026. That is more than Mixin has repaid. Nobody has been named, arrested or charged.