Ethereum Went Through A Chain Split Today And That Is Scary And Encouraging

For a technical explanation of the attack:

https://twitter.com/kelvinfichter/status/1431336698911338496

What's a Chain Split?

A chain split can happen when some nodes view some transactions as valid, while other nodes view those transactions as invalid.

What is a Geth Node?

Go Ethereum(AKA Geth) is one of the more popular implementations of the Ethereum protocol. When someone says they're running a Geth node, that means they are using the Go Ethereum client software on their computer.
When upgrades are made to this software, everyone running Geth nodes must install the upgrade. If they don't they risk their node not processing Ethereum activity like the rest of the network and being excluded because of that.

For a short time today, there were two different Ethereums running.

In a sentence, someone was able to cause a chain split by exploiting an obscure piece of code that caused Geth(one of the most popular clients for running Eth nodes) nodes to see an incorrect return value from that piece of code.

This had implications for other chains too, like Binance Smart Chain, because BSC is an altered version of Ethereum.

The good news is that it took a single line of code to fix this exploit, and everyone is updating their Geth nodes as I'm writing this.

It's pretty incredible that this was found and fixed so quickly and with hardly any network disturbance. Also scary that this can happen. It's a reminder that this is new technology and attackers, a lot of times, are as incentivized or more incentivized to attack a network than the people securing the network are incentivized to secure it.