Bitcoin[note 5][note 6] is a digital asset[16] and a payment system invented by Satoshi Nakamoto,[note 7] who published the invention in 2008[12] and released it as open-source software in 2009.[18] The system is peer-to-peer; users can transact directly without needing an intermediary.[19]:4 Transactions are verified by network nodes and recorded in a public distributed ledger called the block chain.[20] The ledger uses bitcoin as its unit of account. The system works without a central repository or single administrator, which has led the U.S. Treasury to categorize bitcoin as a decentralized virtual currency.[1] Bitcoin is often called the first cryptocurrency,[21][22][23] although prior systems existed.[note 8] Bitcoin is more correctly described as the first decentralized digital currency.[19][26] It is the largest of its kind in terms of total market value.[27]
