Bitcoin is a cryptocurrency and a payment system[13]:3 invented[13]:3,4[14] by an unidentified programmer, or group of programmers,[15] under the name of Satoshi Nakamoto.[16] Bitcoin was introduced on 31 October 2008 to a cryptography mailing list,[17] and released as open-source software in 2009.[14] There have been various claims and speculation concerning the identity of Nakamoto, none of which are confirmed.[16] The system is peer-to-peer and transactions take place between users directly, without an intermediary.[13]:4 These transactions are verified by network nodes and recorded in a public distributed ledger called the blockchain,[18] which uses bitcoin as its unit of account. Since the system works without a central repository or single administrator, the U.S. Treasury categorizes bitcoin as a decentralized virtual currency.[10] Bitcoin is often called the first cryptocurrency,[19][20][21] although prior systems existed[note 4] and it is more correctly described as the first decentralized digital currency.[13][25] Bitcoin is the largest of its kind in terms of total market value.[26]
