Square wouldn't let VeriFone call it out without issuing some sort of statement, and CEO Jack Dorsey has responded to the claims of a gaping security hole in the form of an open letter on the company's website. Dorsey calls its competitor's accusations "not fair or accurate" and says that many of the necessary security measures are already built-in to your credit card itself. He also points out that this sort of credit card number thievery is possible every time you hand your plastic over to a waiter or salesperson, and that its partner bank, JPMorgan Chase, stands behinds all aspects of the service. To us, it seems like Verifone is more than a little scared at the prospect of Square undercutting its fees and potentially upending the POS business -- but we're just theorizing. One thing is for sure though, we'll be hearing a lot more about this as the mobile payment war heats up in the future.