Euler Finance flash-loan attack drains ~$197M

On March 13, 2023, an attacker used flash loans to exploit a missing liquidity check in Euler Finance's donation function, walking off with roughly $197 million and the title of largest DeFi hack of the year. In an unusually civil turn, the thief later returned nearly all of the funds and offered an apology, turning the incident into a case study in on-chain negotiation.