"
The entire ecosystem of Ethereum works on the basis of smart contracts.
The DAO aka the Decentralized Autonomous Organization was a complex smart contract which was going to revolutionize Ethereum forever since it was going to fund all future DAPPS made in the ecosystem.
The community was given also the choice of exiting the DAO. If they wished, then they can do so by sending a request. The splitting function will then follow the following two steps: either give the user back his/her Ether in exchange of their DAO tokens, or register the transaction in the ledger and update the internal token balance.
Unfortunately, on 17th June 2016, someone exploited this very loophole in the DAO and one-third of the DAO’s funds were siphoned away: that’s around $50 million dollars .Following this incident, the community debated the options offered, which were: doing nothing, going with a soft fork or going with a hard fork. They finally went with the latter.
Ethereum classic:
Resulted after the fact that Ethereum platform had been forked into two versions existing simultaneously: Ethereum: ETH, which is the new one, and the old one, which was renamed Ethereum Classic: ETC.
ETC, is on one hand staying true with the philosophy of the immutability of the blockchain, but on the other hand had some flaws. The main problem with the ETC was the lack of backward compatibility with the Ethereum Hard Fork and anyone who is part of the ETC couldn’t be able to access any of the updates done by the ETH. However, ETC’s team have recently made their VM (Virtual Machine) and clients compatible with Ethereum and it’s Byzantium hard fork.
"
rede here https://en.decentral.news/2018/02/06/etc-will-ever-light-end-tunnel/ also about Callisto Airdrop for ETC holders ...