https://onlycoin.com/support/faq/
Q. What steps does the Coin app take to prevent cards from being added fraudulently?
A. The Coin app requires that you take a picture of the front and back of the card, type in card details, and then swipe the card (using a reader we provide) to ensure the card’s encoded magnetic stripe data matches the card details provided. It is not possible to complete these steps unless you are in physical possession of a card. As an additional safeguard, the Coin app will only allow you to add cards you own.
If this is how this works... it is *VERY* insecure.