A circuit breaker would be a start but given how fragmented the crypto scene is, there should be something. Unlike the stocks that have major markets, Crypto has dozens and dozens of exchanges with new ones coming in monthly. That creates very thin books. I know many people do not think gdax has any blame in this but I disagree. They know how thin their book is and should have systems in place that spread a market sell larger than the book across some time rather than just allow someone to dump it all at once. Unlike other markets where shares have been spread far and wide over decades, crypto has a majority in very few hands. Adding to that the fact that millions of whatever have been stolen, hacked, etc and the anonymous nature of it all, it seems mind blowing that an exchange would allow a market sell above their order book. Anyone trading on margin should know the risks but those with stops were affected as well. In gdax, the stop-limit is hidden under the "advanced" link and maybe it shouldn't be. I actually do think they have some duty to their customers, all of whom pay them fees, to make sure a malicious player is not able to manipulate their system, crash the market and buy individual's assets for pennies. Either way, sure we will see this happen again. It is unavoidable with this many exchanges operating in the same, small, space.