The consensus protocol used by Bitcoin and other distributed P2P networks. It requires a miner to solve the cryptographic puzzle in order to be allowed to add a block to the chain and gain its reward. It requires lots of computational power and heavy use of electrical power.
It is conceived so to incentivize the miner to actively mine and refrain from tampering with the block’s content. The network would reject the altered block and the miner would have wasted processing power and electricity for nothing. It is also a strong barrier against hackers.