Here's what happened: Smart Contract Security

In 2016, The DAO hack stole $50M worth of ETH due to a reentrancy bug. Here's how to prevent it: 1. Use OpenZeppelin's ReentrancyGuard for functions that shouldn't be called twice 2. Apply the Checks-Effects-Interactions pattern - validate, update state, then call external contracts 3. Limit contract dependencies - each external call is a potential attack vector 4. Use SafeMath libraries to prevent integer overflow/underflow vulnerabilities

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