Quote:
Originally Posted by grumpy
nope, works different. They do the charging for thousands of websites, here you can check your last transaction with them. Thats why that link can be very handy.
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The first four digits of a CC are simply the bank identifiers. If you have a user's laster 12 digits, and GeoIP their country, run that against a list of card-issuing banks in that country (normally going to be 10 or less) - bam!
If you're really looking to verify cc#s, check out
http://en.wikipedia.org/wiki/Luhn_algorithm
Note for advanced players: the linked PHP version on that article has some bugs in it.