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