Hacker Steals $610M in Crypto, Then Returns It All

An unidentified hacker breached Poly Network, a decentralized finance platform facilitating peer-to-peer token exchanges across blockchain networks, stealing $610 million in cryptocurrencies in August 2021. The theft marked the largest DeFi hack on record at the time, but the attacker's next move confounded the industry: they gave nearly all of it back.

The stolen funds were distributed across three major blockchain networks. Approximately $273 million in Ethereum tokens were taken, along with $253 million from Binance Smart Chain and $85 million in Polygon stablecoins. The hacker targeted at least 12 different cryptocurrencies in total, exploiting a vulnerability in Poly Network's smart contract calls, according to the platform's forensic investigation.

Poly Network announced the theft and immediately called for action. The platform threatened legal consequences, offered a $500,000 reward for information, and urged cryptocurrency exchanges and token issuers to blacklist the attacker's wallet addresses. The company's statement emphasized that thousands of users had been affected by the breach.

What happened next was unprecedented in cryptocurrency crime. Within a day of the theft, the hacker began returning funds. By the second day, partial recovery was underway, with $4.77 million in assets already restored. The attacker subsequently returned the vast majority of the stolen cryptocurrency, ultimately recovering all funds for Poly Network.

The hacker's methods during the recovery phase were equally unusual. They locked over $200 million in cryptocurrency in an account protected by dual passwords—one controlled by the attacker and one by Poly Network—effectively preventing either party from accessing the funds alone. This forced cooperation ensured the platform's participation in the final recovery process.