The hackers responsible for breaking into HBO and stealing a large amount of data have reappeared with a ransom demand. Along with calling on the company to hand over a presumably large sum of money, they've leaked internal emails and Game of Thrones-related info.
Details about the next GoT episode were leaked, as were the phone numbers on record for some of the show's actors. And the hackers provided administrator passwords for the HBO internal network, further verifying the breach.
We successfully breached into your huge network...HBO was one of our difficult targets to deal with but we succeeded (it took about 6 months). - Hackers
HBO has already confirmed many internal documents were stolen. Though it believes its full email system wasn't breached, thereby limiting the amount of potentially damaging internal info that could appear in public.