Bitcoin[a] (₿) is a cryptocurrency invented in 2008 by an unknown person or group of people using the name Satoshi Nakamoto. The currency began use in 2009 when its implementation was released as open-source software. Bitcoin is a decentralised digital currency, without a central bank or single administrator, that can be sent from user to user on the peer-to-peer bitcoin network without the need for intermediaries. Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, products, and services, but the real-world value of the coins is extremely volatile. Research produced by the University of Cambridge estimated that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin. Users choose to participate in the digital currency for a number of reasons: ideologies such as commitment to anarchism, decentralisation and libertarianism, convenience, using the currency as an investment and pseudonymity of transactions. Increased use has lead to a desire among governments for regulation, in order to tax, facilitate legal use in trade and other reasons (such as investigations for money laundering and price manipulation).