Abstract: A verification method and system for determining whether a holder of a card is authorized to complete a transaction through an on-line terminal of an institution in a network of cooperating institutions, such as banks. The method and system are also useable in such applications as accessing a security data file in a computer, entering a security area, completing a point of sale transaction and operating on-line automated tellers in banks. In the preferred embodiment, the card contains information including first data identifying the institution holding an account of an authorized card holder and second data identifying the account. The first and second data are machine read from the card and a secret number, derived from the data but known only to the authorized holder of the card, is keyboard entered by the card holder. The first data are used to address a read only memory having random characters stored therein.