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...http://www.google.se/patents/US4667087?utm_source=gb-gplus-sharePatent US4667087 - Secure credit card
