What was the DAO hack on Ethereum?

The DAO hack on Ethereum was a significant event that shook the cryptocurrency world in 2016. The Decentralized Autonomous Organization (DAO), which was billed as a groundbreaking experiment in decentralized governance and funding, suffered a major security breach. Hackers exploited a vulnerability in the DAO's smart contract code, enabling them to withdraw over 3.6 million Ether from the organization's funds. This attack highlighted the risks of deploying untested and potentially flawed smart contracts on the blockchain, and it sparked intense debate about the future of decentralized applications and their security. The hack led to a hard fork of the Ethereum network, splitting the community into two separate blockchains: Ethereum Classic, which upheld the original chain, and Ethereum, which implemented a change to reverse the hack and refund investors.