A hacker who robbed the decentralized stablecoin platform Beanstalk in April had a powerful tool: a $1 billion loan taken out with no collateral, no proof of income and no identity verification. The loan had to be repaid in less than a second, but that was all that was needed to steal tens of millions of dollars.
The hacker used what is called a flash loan—a cheap, instant and anonymous form of financing based on cryptocurrencies.
Source: https://www.wsj.com/articles/this-billion-dollar-crypto-loan-is-easy-to-get-but-gone-in-a-flash-11651985089?siteid=yhoof2&yptr=yahoo