It happened when Ethereum was less than a year old. The hack exploited a vulnerability that was arguably systemic, since it also existed in a lot of the sample

It happened when Ethereum was less than a year old. The hack exploited a vulnerability that was arguably systemic, since it also existed in a lot of the sample code on ethereum.org. When Bitcoin was a little more than a year old, it reverted five hours of transactions after a bug exploit. Both blockchains have matured since then and don't do that anymore. An Ethereum cofounder's company lost over $100M in ETH, and the community refused its requests to restore funds with a fork.