Originally Posted by
manneca
I think it's the cc maker. I've had my Cap One and my CSP and Chase United card both compromised just after I received a new card. In all cases, fraud caught it immediately.
I think it is someone simply guessing credit card numbers. Numbers are issued in blocks and the algorithm to calculate the checksum is well known, so it is fairly easy to generate a valid credit card number.
The difficult part is guessing the expiration date and the CVV. The fact that Chase is usually catching those transactions is likely because the fraudster doesn't have the correct CVV or expiration date. They conduct a couple of small test charges. Of course some merchants (like Amazon!) don't even check the CVV, so you only need the expiration date.
The reason why Chase is hit so often is also simple: they issue a lot of cards, so they have a large block of credit card numbers. The probability that someone guesses a Chase number is thus higher than for other issuers.