A hacker who robbed the decentralised stablecoin platform Beanstalk in April had a powerful tool: a $1bn 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.