That happened to me a while back, too. The Mac store called to verify my iPod order. Well, I hadn't ordered any iPods. I quickly called Citicards. Someone had racked up about $1000 in electronics that I hadn't bought. They were really good about cancelling those charges.

Another nice thing about the Citicard is that they have a "virtual" card. If you order online it generates a new number for each purchase, so the card number can't be stolen. I like using my card online more than in a store now.