Originally Posted by Giggleton
It implies that Pottermore will be storing your credit card information on its servers so that you may be periodically charged in order to continue your Harry Potter experience.
No, it means that when Eric Schmidt calls your name the tattoo on your arm will itch and burn.
Obviously you should keep your credit card locked in a safe and never
let anyone know the magic number, especially people who might use it to sell you something!