Electronic money circulated on the Internet. Currency unit is BTC. Since banknotes and coins are not issued, they are also called ""virtual currency"" or ""digital currency"". There are no business entities or states that manage distribution, and there is nothing like a central bank. Exchanges with real currencies such as US dollars and yen are made through ""exchange"" on the web, but because the settlement does not pass through financial institutions, various expenses, fees, etc will not occur. For that reason, it is used for small trading and P2P (individual-to-individual) transactions, in particular remittance and settlement across national borders. In May 2009, a person named Satoshi · Nakamoto announced its principle in a paper and hackers who sympathized with ""non-centralized"" mechanism developed and disseminated. Satoshi · Nakamoto's identity is unknown. Issuance of currency is done through work such as ""mining"" where users solve sophisticated arithmetic problems. However, the computation processing is designed to become more complicated as the issuance volume increases, and it can not create more than 21 million BTC. Originally, IT (information technology) experts and maniacs gathered in some net spaces gathered, but gradually became adopted for settlement by major enterprises, Cyprus finance that became apparent 11 - 12 years In the crisis, attention was gained as a stable currency close to ""gold"". The exchange rate with the real currency is subject to the influence of the supply and demand and the economic situation, and it is susceptible to speculation, so it is repeating the volatility. In addition to these exchange risks, there are also criticism that it is a hotbed of illegal transactions such as money washing. However, ease of use and convenience are popular, and in April 2013, only four years from development, it has grown to more than $ 1 billion in circulation volume.