A tamper-proof ledger is essentially any system of records that has the fundamental properties of a blockchain distributed ledger.
Blockchain technology relies heavily on security, which is why in theory, all blockchain ledgers are tamper-proof ledgers. The monetary system we currently operate with on a global scale consists of numerous ledgers. Banks and credit card companies are essentially ledgers at their very core - they store information about transactions, and the way money moves between parties. Unfortunately, the traditional banking system is often put under pressure because of the high risk of fraud and information tampering.
This is where blockchain technology or tamper-proof ledgers come into play. The first truly successful tamper-proof ledger came with the introduction of the Bitcoin whitepaper. Satoshi Nakamoto details a revolutionary idea of how to ensure the Bitcoin ledger will remain tamper-free.
While previous attempts at creating functional decentralized financial systems all focused on prohibiting tampering with the ledger, Nakamoto realized that it is sufficient just to incentivize users not to tamper with the ledger. This means that Bitcoin, specifically the Bitcoin blockchain, discourages tampering because this would mean automatic exclusion from the network. In essence, node operators responsible for validating transactions and thus adding new blocks to the chain are actively discouraged from tampering with the records because such a change will be easily detected. As a decentralized network, all Bitcoin node operators validate transactions based on the same copy of the ledger. If someone tries to tamper with the records, their copy will not match that of the remaining node operators; thus, consensus will not be achieved. If a node’s copy of the record does not match and there is no consensus, the node becomes inactive.
In essence, Bitcoin is the first natively tamper-proof ledger, as it discourages nodes from altering the records. If a node ceases to be in consensus with the rest of the network and becomes inactive, the node operator stops receiving mining rewards. In other words, Bitcoin node operators have no reason to tamper with the ledger, or they will stop receiving Bitcoin rewards.
Since Bitcoin first launched in 2009, many more blockchains have been created. Regardless of the consensus mechanism behind them, all of them rely on incentivizing note operators not to tamper with the records. This incentivization mechanism ensures that the distributed ledger remains tamper-proof regardless of how much it grows and how many blocks are added to it.