Each new block that is generated is checked by every single computer in the network before it is incorporated into the existing chain. verified. Subsequently, the new block encrypted and appended to the previous blocks. In addition, at the beginning of a new block there is always a Summary of the previous block so that each block always refers to its predecessor.
Since later transactions always refer to the ones before them and thus verify them again, it is impossible to manipulate or delete a single transactionwithout also changing all the blocks that come after it. Every participant in the network could see this inconsistency of the successive blocks.
This combination makes it impossible to change, copy or delete individual pieces of information on a blockchain. This makes blockchains secure, always up-to-date directories that can document digital transactions in a traceable way.