This domain name sharkhide.com/cart

I installed the guest checkout and it works great...Had it up for awhile, well someone just noticed that if you add something to the cart and then go through the process and once you get to the payment page,,if you click on "change shipping address" or "change billing address" it will show you other customers contact info (near the bottom)....not good, I have no idea how to fix this...any help would be appreciated

thanks