A method of preventing removal of a smart card having a counter zone associated with a first reference zone, and a balance zone associated with a second reference zone. The counter zone has at least two levels of counters, each having at least two bits. The counter zone is operable in accordance...http://www.google.com.tw/patents/US5847374?utm_source=gb-gplus-share專利 US5847374 - Smart card having a plurality of data fields with reference zones and validation bits 
