How would you prevent mass credit card theft in this case? Couldn't an unscrupulous person, say a waiter at a restaurant, take your card, use his/her own Coin to make a copy of your card, add it to their own Coin, and then use that card at their leisure at a future date? I know, the same question was asked re: Square and the like, but the difference is that you need a Square account to steal other people's cards, and that's traceable, whereas here, you can use the stolen card easily and surreptiously with little notice. Except for the fact that using a Coin in itself is noticeable.