 Typically, a legitimate smart card is attached to a host digital television receiver, which is equipped with software to share the decrypted 64-bit "control word" key over a computer network, such as the Internet.Once a client receives this key, they can decrypt the encrypted content as though they were using their own subscription card.The theory of card sharing as a potential attack vector on pay TV encryption was provided in the book "European Scrambling Systems" by John McCormac in 1996; leading to the term "McCormac Hack" to be used to describe early card-sharing systems.