Can smart contracts be modified or deleted once they're deployed?

Once a smart contract is deployed on a blockchain like Ethereum, it cannot be modified or deleted by anyone. This immutability is a core feature of blockchain technology—the code becomes permanent and transparent for all to see. However, developers can create upgradeable contracts using proxy patterns, which allow them to redirect code execution to new versions while keeping the same address. If a contract has bugs or vulnerabilities, users' funds can be at risk since they cannot simply "fix" it. This is why security audits are crucial before deployment. Some contracts include self-destruct functions, but these are rare and typically require specific conditions. Understanding this permanence is essential when interacting with smart contracts, as you're trusting the original code's security.