Bitcoin is a worldwide cryptocurrency and digital payment system[9] called the first decentralized digital currency, as the system works without a central repository or single administrator.[9]:1[10] It was invented by an unknown programmer, or a group of programmers, under the name Satoshi Nakamoto[11] and released as open-source software in 2009.[12] The system is peer-to-peer, and transactions take place between users directly, without an intermediary.[9]:4 These transactions are verified by network nodes and recorded in a public distributed ledger called a blockchain.