This is why I never use a credit card on the internet, I used to work CC frauds it is just to easy to get hacked everything you put into your computer can be gotten to, so it may not have been a vendor who got hacked.
If I am doing business with an internet vendor.(and I just about have to where I live) I will try to do it by USPS and check or money order, I have found very few ebusinesses who do not want to do business that way and if they don't I find sombody who will.
Oh and by the way you are not liable for fraudulent CC charges. you will have to surrender your cards and get new ones with new acct. numbers though.