blockchain transactions are validated and processed by participants that are already recognized by the ledger.
In some aspect there is still challenges and issue of trust around it as well
now before one can be rest assured he has to verify that the blockchain is secured and trustworthy in order to avoid the substantial impact of a cyberattack.
Another reason for this is by building security into your blockchain technology through strong authentication and cryptography key vaulting.
Provide strong identities and authentication to gain access to the blockchain.
A blockchain does not protect your privacy. Since usually, everything can be looked up directly for everyone, you have to keep anything you want to keep private away from a blockchain.