Look at the error messages in this screenshot
Now look at the available blanks on the form.
This was corrected when I went back later
I never seen anything like that before. Along those lines, once I logged into Bing Adcenter and I was looking at someone else' account data -- full access.
They must have been testing something and accidentally went live with it. I mean, who asks for your Social Security Number on a credit card form? Something seriously wrong.
Phone co's in the US routinely ask for SSN for a credit check when signing up for service. Probably an alternative view in the app that requires SSN and like you said went live with a bug.
I once had Googlebot rent movies for me on Netflix, and another user had their credit card and profile showing in Yahoo cache. Cloaking and user authentication gone horribly wrong.