I just read this morning that there was a crazy glitch on Coinbase where anyone could have coded up a smart contract, which exploited a bug on Coinbase to give themselves unlimited free ether.
The bug was reported by a company in January but there may have been a few people who got very rich off this bug before it was caught!
Here's a link to the article I was reading:
https://thenextweb.com/hardfork/2018/03/21/coinbase-smart-contract-bug-allowed-crediting/