Bitcoin, Ethereum, and most of the projects out there have never had their protocol compromised. There are a few exceptions -- the biggest ones being Ethereum Classic (ETC) and MIOTA. ETC had their protocol compromised by a 51% attack, MIOTA's system is most likely not even a real blockchain, after being audited by the MIT Technology Review. But we call them "zombie chains" because the blockchain allows for these projects to persist, even though it's dead.
