The Ethereum platform has been forked into two versions: "Ethereum Classic" (ETC) and "Ethereum" (ETH). Prior to the fork, the token had been called Ethereum. After the fork, the new tokens kept the name Ethereum (ETH), and the old tokens were renamed Ethereum Classic" (ETC). Ethereum Classic appeared as a result of disagreement with the Ethereum Foundation regarding The DAO Hard Fork. It united members of the Ethereum community who rejected the hard fork on philosophical grounds. Users that owned ETH before the DAO hard fork (block 1920000) owns an equal amount of ETC coin after the fork.
Ethereum Classic underwent a technical hard fork to adjust the internal pricing for running various op codes on the Ethereum Virtual Machine (EVM) on 25 October 2016, similar to the hard fork the ETH chain did a week earlier. The goal was to more rationally price various compute-intensive and external reference commands to reduce the incentive for spammers who had conducted a month-long distributed denial-of-service attack on the Ethereum Classic network.