This final note comes by way of Businessweek:

The FBI says criminals have found a new way to use stolen credit cards. They scale the roof of a store and wrap aluminum foil around antennas. Stores use antennas to communicate with credit card companies. That foil blocks the transmission, which means stores can’t verify whether a card is legit or stolen. 

Businesses figure the connection’s down temporarily, which happens every once in a while, and approve the transaction.

By the time a business finds out what the card was stolen, the criminals are long gone with the merchandise they bought and the stores … are on the hook.