A credit card resistant to unlawful use has a code, indicative of the owner's account number hidden beneath an opaque shield. The card has a keyboard and microprocessing components electrically connected to the shield. Insertion of correct entries, e.g. an owner's personal identification number, into the keyboard results in application of an electric signal to the shield to render it transparent in order that the code may be viewed by another person or by a machine. Erroneous attempts to operate the keyboard beyond a predetermined standard disable the keyboard from further operation.