Mastering Blockchain Programming with Solidity

Immutability

Every transaction that happens on the Ethereum blockchain is immutable. Smart contracts on the Ethereum blockchain are also immutable. Once the smart contract code is deployed, it cannot be changed. Smart contract code will remain on the blockchain forever. Anyone can see any deployed smart contract any time in the future as well, just by putting its contract address on the block explorers. Data that is being stored in smart contract variables is also immutable, unless there are data removal techniques that have not been exposed by the contract code.