If I had a dime for every time I’ve been asked, “How do I protect my credit card number?” I’d be living on my own island in the Pacific. My response has always been, “Use your card whenever and wherever and don’t worry about it, but pay close attention to your statements,” because that’s really all you can do.
http://robertsiciliano.com/blog/2013/02/14/billguard-is-personal-finance-security/