A proof-of-workAdam Back is the inventor of hashcash, which is a proof-of-work system used by several anti-spam systems. It in turn inspired a similar system in bitcoin. is a system that ties mining capability to computational power. Blocks must be hashed, which is in itself an easy computational process. When a block is successfully hashed, the hashing must have taken some time and computational effort. Thus, a hashed block is considered proof of work.