Typically by making a small (fradulent) purchase at an innocent merchant and seeing if it works.
This is illegal because of the fraud. It harms the merchant in all sorts of ways, and also the cardholders and issuers.
This is illegal because of the fraud. It harms the merchant in all sorts of ways, and also the cardholders and issuers.
That's going to be in records of accounts that eventually report compromises, and get figured our pretty quick, I'd imagine.