Community Submission - Author: Caner Taçoğlu

Immutability means unchangeability. In computer science, an immutable object is an object whose state cannot be altered after its creation. 

Immutability is one of the key features of Bitcoin and blockchain technology. Immutable transactions make it impossible for any entity (for example, a government or corporation) to manipulate, replace, or falsify data stored on the network. 

Since all historical transactions can be audited at any point in time, immutability enables a high degree of data integrity.

The immutability of public blockchains can enhance the current trust and audit system. It can reduce the time and cost of audits since verifying information becomes much simpler or effectively redundant.

Immutability can also increase the overall efficiency of many businesses by providing them with the opportunity to maintain a full historical record of their business processes. Immutability can also provide clarity to many business disputes, as it enables a verifiable, shared source of truth. 

While immutability is one of the core benefits of Bitcoin and blockchain, the data stored on blockchains aren’t completely resilient to vulnerabilities. If a malicious actor is able to amass the majority of the network hash rate, it could alter the otherwise immutable data in an attack called the 51% attack. 

In such a scenario, the attacker would be able to prevent new transactions from gaining confirmations or even reverse transactions entirely. However, at least in the case of Bitcoin, gaining control of this amount of hashing power would be hugely expensive, requiring substantial hardware and considerable amounts of electricity. 

On the other hand, Proof of Work networks with lower hash rates are vulnerable to such an attack, as collecting the required amount of hashing power to attack the network isn’t such an unreasonable feat.