Bitcoin is a worldwide cryptocurrency and digital payment system[8]:3 called the first decentralized digital currency, as the system works without a central repository or single administrator.[8]:1[9] It was invented by an unknown person or group of people under the name Satoshi Nakamoto[10] and released as open-source software in 2009.[11] The system is peer-to-peer, and transactions take place between users directly, without an intermediary.[8]:4 These transactions are verified by network nodes and recorded in a public distributed ledger called a blockchain.