BCOM are not processing the payment here. They provide a "Hotel Login" which then let's the hotels view (upto N times) the raw card information of the guest for use internally on their own payment processes. There's various approaches that they make available, this is one of a few. More recently Booking.com started to move away from providing the raw card information and instead providing a virtual card which "Activiation" date only becomes enabled once the cancellation policy for the guest booking kicks in (allowing the hotel to charge before arrival). There's also an API approach, but the leading way to get access to the card/payment information __because__ BCOM are not merchants here is to provide this to the merchants/hotels through a BCOM login page. Reading between the lines, this is what I think was exposed.