A blockchain is a public ledger of all cryptocurrency transactions. Each group of transactions are referred to as a block, with each block then being combined chronologically into a chain. Information that exists on the chain is shared and public, therefore, every node connected to the network, possesses a copy of the chain. Each node will be able to have access to all transactions that have ever taken place, or will take place on the chain. The distributed nature of blockchain technology also means that the database cannot be controlled by a single entity, nor can it easily be hacked as there is not one single point of failure. Unauthorized changes to the chain would be unlikely, as overriding the network would require a tremendous amount of computing power.