Blackmail is a possibility. However, most hackers do this kinda shit for the lulz. I can see Mason wanting to protect his forum by shutting it down until a security team he hires gets to the bottom of exactly what exploit was used. At that point they will have some work to do to protect against it and that takes time. There is no doubt in my mind that they keep very regular backups and that when it comes back up it will be complete.

It's wishful thinking to assume that a hacker with an agenda to embarrass them did the job. I hope it is though.