$BTC A necessary and sufficient element of this payment system is the basic client program (it is open source). Client programs launched on multiple computers connect to each other in a peer-to-peer network, each node of which is equal and self-sufficient. One of the consequences of decentralization is the potential possibility of 'double spending', that is, transferring the same bitcoins to different recipients. Under normal conditions, this is protected by including the transaction in the blockchain. However, if more than 50% of the total computational power of the bitcoin network is controlled, there is a theoretical possibility of 'replacing' one chain of transactions with another.