It's well known that one of the first thing tech-savvy gamers look on when analizing the assets of a videogame is for how to turn the characters nude. It happened in The Sims, it happened in Tomb Raider, it happened in Dead or Alive, and it has happened again in Final Fantasy XIII.
Apparently, browsing through the assets on FFXIII's disc, the site MADOKA Park! stumbled accross the model of a naked Vanille. This is used during the game in a scene where Vanille appears as she came to the world (but don't go thinking anything or preordering the game just to see that, she's covered in that scene, I guess you'll have to blame the camera like in most games).
Still, this doesn't change the fact there's a nude asset of Vanille, so I wouldn't be surprised to find out hackers working on a nude-patched 360 version of FFXIII when it comes out (sorry, PS3 gamers, you're out of luck until the PS3 is hacked). Square-Enix knows perfectly how some gamers are fascinated with their characters, and seems like they decided to give them even more to be fascinated with