I don't know why you guys are worrying so much. At worst case, if you have fraudulant charges on your credit card, it's nothing more than a short amount of time to reverse the charges and, if your bank tries screwing you, $50 out of your pocket (which is highly controversial since all banks are required, by Federal low, to protect any and all reserves you have, be it money or your charge card).
Just do the following:
1) Contact the organization that made the charges and politely inform them that you did not make or authorize that purchase and would like an immediate refund.
1b) Since they'll probably say they want to investigate it, they'll tell you that they require some time to look into it. Respond by informing them that you, in fact, did not make or authorize the said purchase and that it was their policies, procedures, methods, whatever that allowed somebody to fraudulantly use your credit card. Had they verified that their customer had actually been authorized to use the credit card, the problem would not have occurred. Therefore, if they refuse to refund your money immediately (give them 7 days as most organizations can only do credit card refunds once a week), then you will simple have the credit card company refuse the charge (this is much worse for the company in the long run).
2) If the company doesn't refund your money, contact your credit card company (use the 1-800 number for Customer Service or whatever it's called on the back of your credit card) and inform them that there has been a/some charge(s) made with your credit card and you need to take the steps necessary to get this money back. (Most will probably give you an address and ask you to explain the entire situation in writing with a signature and you will get your money back, at the latest, in a month.)
IF THIS IS A DEBIT CARD:
1) Contact your bank first and inform them in case you begin to have overdrawn or other fees charged to you, as to keep them from piling up (with some assholish banks, you may need to remind them of their Federal obligation to protect your money).
2) Repeat most of the steps stated above.