Immutable

Immutable describes data that, once written to a blockchain and confirmed, cannot practically be altered or removed. The history is effectively permanent.

How it works

Each block includes a cryptographic fingerprint of the block before it, so changing an old record would change its fingerprint and break every block that follows. To rewrite confirmed history an attacker would have to redo the network’s accumulated work or stake and overpower the honest majority — economically irrational on a large chain. Immutability is therefore a practical guarantee backed by cost, not a magical absolute.

Why it matters

Immutability is what lets strangers trust a shared record without a referee: no one can quietly edit balances or erase transactions. The flip side is that mistakes and theft are also permanent, which raises the stakes on writing correct smart contracts and guarding keys.

Example

Once a payment has enough confirmations, it becomes part of the immutable ledger and cannot be reversed.