How does the security of a block works?

• A blockchain is a series of blocks that hold transaction information. The most secure portion of a blockchain is the block. A cryptographic hash algorithm is used to secure a blockchain's record. Each block is linked to all previous and subsequent blocks by a unique hash pointer, which increases the block's security. When a value within a block is changed, the hash value changes as well. This hash is a security identifier that gives the entire blockchain a fair level of protection.
• To modify the block information, ambitious hackers also need to know the prior block's hash key. Blockchains are decentralised and spread across peer-to-peer networks that are constantly updated and continually syncing for those ambitious hackers. Blockchains have no single point of failure and cannot be modified by a single machine because the records are not stored in a central location.

Read More: Is it possible in Blockchain to remove one or more block from the networks?