Finney Definition: Finney, named after Hal Finney, refers to the first successfully known cyber attack on Bitcoin, which Hal Finney discovered. For this reason, this was named after him and enabled the possibility for double spending to occur. Due to this discovery, this historic attack was called Finney, and is now known as a hack that allows a person or entity to double spend or effectively steal cryptocurrency from an unsecured wallet or storage.
This process was explained in simple terms. The Finney hack is done through mining when a transaction is performed from one address to another, where both belong to the same person. Another purchase with the same currencies can be duplicated or taken and used by another user. When cryptocurrencies are effectively stolen from the original user, the hacker can double spend and claim ownership of the assets.