Immutability is the core defining feature of blockchain. The word 'immutable' means that data cannot be changed or modified by anyone after its creation.

In a blockchain network, there is a need for immutability because all the nodes have to agree on the validity of the data before passing it on. The whole point of using a blockchain as a distributed ledger technology (DLT) is to ensure that no individual entity can make changes to records once they are added to the blockchain.

It's the ability to record transactions such as contracts, sales, purchases, etc., in such a way that once they are added, the data in those records cannot be altered retroactively without the alteration of all subsequent blocks and the collusion of the network.

How Blockchain Is Made Immutable?

Cryptographic hashing is what makes blockchain immutable.

Hashing is an encryption technique that takes plaintext input of any length and produces a unique hash value. Hashes are always of a fixed length, regardless of the properties of the input they are based on.

The hashing algorithm is very simple, yet surprisingly difficult to reverse. For example, if you applied the SHA-256 hashing algorithm to the phrase "the quick brown fox jumps over the lazy dog", it would return a 256-bit (64 characters) hexadecimal number like "ebc637e1a3b4902dce844b8c1e1014f11ccb0d4e0240071aae71d453c3c509b5". If you were to apply this algorithm to any other string of text (for example, your password), you will always get the same output (a 64-character hexadecimal number).

The hash can be used as a digital signature for data integrity purposes. 

When we send some data over the network, we can use its hash value as a fingerprint. If we receive the same data we can compute its hash and verify if it's equal to our original fingerprint. If not, we know that someone tampered with our data while it was in transit.

It’s important to note that immutability doesn’t guarantee that data can’t be altered. Its purpose is to merely ensure that no data or record on a blockchain can be altered without consequences.

Benefits of Immutability 

The benefits of immutability are related to security, data integrity, easy auditing, and fraud prevention on blockchains. 

In a traditional database system, if someone gains access to the data, they can corrupt or destroy it. In a blockchain, any changes to data require that all nodes on the network adopt the change. This is why there is no risk of data loss in a blockchain and why it is considered immutable. 

Blockchain immutability ensures the protection of data integrity. The integrity of a chain can be validated simply by re-calculating the hashes value. Any discrepancy between the block data and its corresponding hash value indicates invalid transactions. 

Because of immutability, an organization can produce an indisputable ledger, which prevents them from facing complications during an audit. 

Thanks to cryptographic hashing, blockchain is immutable. Any changes or alterations made to a chain will disrupt the whole network. 

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