Last year in April, the first and one of the most successful ICOs to date was launched, the DAO (Decentralized Autonomous Organization). Through its month-long ICO, the project raised about $168 million. Afterwards, an attacker was able to exploit a vulnerability that allowed them to make away with almost a third of ether tokens. Those 3.6 million ether or so had a value of over $50 million at that time.
Most of the Ethereum community wanted to create a fork to allow a refund back to investors, while others insisted that the code not is interfered with. In the end, a hard fork was implemented, causing the two versions of Ethereum based on the same blockchain. At the fork, an Ethereum holder would also become an Ethereum classic investor. This was later observed this year when bitcoin forked to create bitcoin cash.