Photos of every page of the book were leaked (either an advance copy or one that was sold early), so it looks like the leak is legit (as opposed to a hoax). Apparently, the publisher spend $20 million attempting to keep the book secret. Don't know what that entails, but they clearly didn't get a very good value.

If it was an advance copy, whoever leaked it will be sued for breach of contract. Same goes for any store that sold the book early. If the leaker just bought a copy from a negligent retailer, then they could probably only be sued for copyright infringement, which really doesn't cover the main source of "damages" in this case.