1. 7 Eleven-American Express Internet Shopping Card.
http://www.7-eleven.com/products.html
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2. 7 Eleven-American Express Internet Shopping Card Balance Check.
http://www.7-eleven.com/products/card_bal.html
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3. 7 Eleven-American Express Internet Shopping Card F.A.Q.
http://www.7-eleven.com/products/AMEX_12_13.html
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4. Julia Angwin. Credit-card fraud has become a nightmare for e-merchants, September 19 2000. Wall Street Journal Archives.
5. ANSI X3. 92-1981, Data Encryption Algorithm, American National Standards Institute, New York, December 31, 1980.