Originally Posted by ozstamps
"Impossible"? You are kidding right?
Most cards issuers haver a typical 3 year rolling expiry regime. i.e. get a new card now and for most banks it will expire September
2008 or a year further for some.
So you have about the same chance or guessing the right expiry as winning at roulette betting on a single number. And those odds are pretty good - ask anyone in Vegas.
The 3 or 4 digit non-embossed check letters were partly devised to add hurdles to the math probability of guessing, but if all they asked was
expiry date, you can invent any number you want changing last few digits of a real card, and you'll be right a few % of times - guaranteed.
I do not agree with another comment above. I think it is likely it
IS held against another real card, and for that reason I'd cancel it ASAP or the UA fraud division might well come down on you if that customer complains.
This isn't what I said. A check digit is in the actual 16 digit number of the card. The last digit or two is the result of some complicated formula based on the previous 14 or 15 digits. The same is true of the little numbers on the bottom of barcodes. So, if 1234 5678 9012 345
6 is a valid number, then 1234 5678 9012 345
7 will not be.
http://www.merriampark.com/anatomycc.htm (scroll down to Check Digit)