Cryptocurrency - choose a jigsaw puzzle to solve

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.