What are Crypto's and really they worth it !! A cryptocurrency (or crypto currency ) is a digital asset designed to work as a medium of exchange that uses cryptography to secure its transactions, to control the creation of additional units, and to verify the transfer of assets. [1] [2] [3] Cryptocurrencies are classified as a subset of digital currencies and are also classified as a subset of alternative currencies and virtual currencies . Bitcoin , created in 2009, was the first decentralized cryptocurrency. Since then, numerous other cryptocurrencies have been created. These are frequently called altcoins , as a blend of bitcoin alternative . The decentralized control is related to the use of bitcoin's blockchain transaction database in the role of a distributed ledger .