Online Credit Card Number validation

I was just thinking how a site that requires a credit card number or a VISA Card or any other card to register or do any other think validate the number and the CvC code. Is there an algorithm on satisfying which the Card number and CvC code are validated or do these sites query the VISA site if the number and CvC code are correct?

http://www.merriampark.com/anatomycc.htm It sounds like the easiest way to check would be to calculate the Luhn checksum; if it matches it might be good…

That can't possibly be the only check they do. What else do they do?

They could check with visa. From my understanding that is just the fast way, but at stores there is a delay before your card goes through. It's checking that it's valid

cyb3rl0rd1867 wrote: They could check with visa. From my understanding that is just the fast way, but at stores there is a delay before your card goes through. It's checking that it's valid Pretty sure they do more than just check if the number is valid. Otherwise how would your credit card ever be rejected when there's a hold on your account?

ynori7 wrote: [quote]cyb3rl0rd1867 wrote: They could check with visa. From my understanding that is just the fast way, but at stores there is a delay before your card goes through. It's checking that it's valid Pretty sure they do more than just check if the number is valid. Otherwise how would your credit card ever be rejected when there's a hold on your account?[/quote] It checks with visa that it's a valid account