I had something similar occur a few months ago. I had my citi credit card account converted to a different one (rewards account). After receiving the card, it never left my house. I used it for online purchases only, and most of those were made using the citi "virtual card numbers" service (a one-time use card number with dollar amount and/or time limit). Somehow someone tried to make an online charge against my account (using the true card number) but the transaction was halted because they used an incorrect card expiration date. I used the real card info only at two online retailers - Amazon and NewEgg. The attempted fraudulent charge was at some small online clothing or shoe store. I know credit cards aren't totally "random" numbers and there is some sort of algorithm involved. I used to have a little app that could check a number for viability.