I just dicovered the existence of the Luhn algorithm Very cool.
http://en.wikipedia.org/wiki/Luhn_algorithm
Here is a Java impl:
http://www.darkcanyongroup.com/code/luhn_algorithm.txt
We should have a built-in validator for this.
need translation
invalid credit card number
brazilian portuguese (pt-br): número inválido de cartão de crédito
Danish/DK: ukorrekt kreditkort nummer
de-DE: ungültige Kreditkartennummer
it-IT: "numero di carta di credito invalido"
es-ES número de tarjeta de crédito inválido
need translation