How do we ensure data Immutability?

Immutability is the ability for a ledger to remain a permanent, indelible, and unalterable history of transactions

But first, let's explain what is a hash.

Hashing is simply passing some data through a formula that produces a result, called a hash. That hash is usually a string of characters and they are always the same length, regardless of how much data you feed into it. Hashing works in one direction only – for a given piece of data, you’ll always get the same hash BUT you can’t turn a hash back into its original data.

We chain transaction logs thanks to their hash.

The first transaction will come with a hash made from its data, then the following transaction produces a hash from it’s data and the previous hash and so on.