A blockchain is solely a chain of blocks that contains information. Each block has a cryptographic hash of the previous block, a timestamp, and transaction data.
Although the design is simple, it is this design that makes Blockchain invulnerable to data tampering.
Blockchain technology is an open distributed ledger that can record transactions of two parties securely and efficiently. As it is distributed, Blockchain is typically managed by a peer-to-peer network working simultaneously together to solve complex mathematical problems in order to validate new blocks. Once recorded, the data in any given block can’t be updated retroactively without changing all subsequent blocks, which requires the confirmation of the majority in the network. this is the main reason why blockchain technology is secure and not susceptible to hacking.