If you're a Tales fan, you probably want to avoid digging too deep into the internet, as you're likely to come upon a rather large number of spoilers Tales of Xillia. Details about the game's story have been leaking out over the past week, just ahead of the game's September 8 release.
There were initially a number of theories about the cause of the leaks. The natural assumption was that someone had gotten the game early. Later, it was widely reported that an official "scenario book" bonus item had that was to be released with the game's Korean version had leaked out.
Namco Bandai released an official statement about the issue today. The source of the leak is a major Korean publisher who will be publishing a guide to the to the game. Portions of the guide were leaked out onto the internet in advance.
Namco Bandai also denied the claims about a "scenario book" bonus item. There's no such item.