[gTen]

It could not be a google market place as they all use Google Checkout...the people who receive the money get it in their accounts and are paid by Google...It is not possible for it to be stolen there...

did you use the card offline at all? or at an ATM?

Maybe you visited an online site that placed a Trojan and/or keylogger on your pc or there was that Flash exploit recently as well..

or maybe they had your number for a while and chose to use it month later to cover up their tracks...