A cryptocurrency (or crypto currency) is a controversial digital asset designed to work as a medium of exchange that uses strong cryptography to secure financial transactions, control the creation of additional units, and verify the transfer of assets. Cryptocurrency is a kind of digital currency, virtual currency or alternative currency. Cryptocurrencies use decentralized control as opposed to centralized electronic money and central banking systems. The decentralized control of each cryptocurrency works through distributed ledger technology, typically a blockchain, that serves as a public financial transaction database.
Bitcoin, first released as open-source software in 2009, is generally considered the first decentralized cryptocurrency. Since then, over 4,000 altcoin (alternative coin) variants of bitcoin have been created.