HBO files labeled as “confidential” were posted publicly online Monday, according to the Hollywood Reporter. A script summary for an upcoming episode of the network’s premier series, Game of Thrones, was also uploaded.

The hackers are now demanding a ransom for the rest of the material, while HBO is conducting a “forensic review” to figure out the extent of the problem.

Here’s everything you need to know about the HBO hack.

Who are the hackers?

We don’t know exactly who they are, but we do know a little about them.

Someone going by the name of “Kind Mr. Smith” emailed a number of recipients Thursday claiming to be involved in the attack. In the email, which THR also received, Kind Mr. Smith wrote that “HBO (specially Poor Richard) is Bluffing. We have ‘STILL’ full access to their webmails….” That’s likely a reference to a memo Plepler wrote to employees saying that “we do not believe that our e-mail system as a whole has been compromised.”

Kind Mr. Smith vowed to release more content from the hack on Sunday, but that didn’t happen. THR received another email later that evening claiming that the material wasn’t being released because “some of HBO’s top competitors are negotiating with us for buying the dump.” But that’s unlikely, as rival networks could face serious legal consequences for purchasing such illicitly received content.

It’s also unconfirmed if Kind Mr. Smith actually has anything to do with the hack beyond his emails to THR.

What do the hackers have?

The hackers claim to have 1.5 terabytes of HBO data, which is roughly seven times more than the hackers who targeted Sony in 2014 got.

The stolen HBO data allegedly includes scripts, episode summaries and marketing materials for Game of Thrones, which is in the midst of its penultimate season. Unaired episodes of other network shows, Ballers and Room 104, were also posted online. Leslie Cohen, the network’s vice president for film programming, had about a month’s worth of emails stolen, but the content of those messages has not yet been revealed.

But those materials alone aren’t likely to add up to 1.5 terabytes of data. So what makes up the rest of the cache, assuming the hackers actually do have that much information, remains unknown.

What do the hackers want?

Money, apparently. When the latest data dump came on Monday, “Mr. Smith” also included a video message addressed to Plepler demanding that HBO pay a ransom of “our 6 month salary in bitcoin,” which they implied would amount to at least $6 million, according to the Associated Press.

Bitcoin is a digital cryptocurrency that is accepted by a number of international retailers, including Microsoft, PayPal and Overstock.com. The currency has made headlines in recent months for achieving record value. A single Bitcoin is worth almost $3,500 at this time of writing. Bitcoin is used by many computer criminals because it’s difficult to trace.

Why are they targeting Game of Thrones?

The hackers did not give a specific reason as to why Game of Thrones was being hit particularly hard by the cyberattack. But it’s likely because the fantasy drama is HBO’s marquee series, and thus represents the entire network. The hackers alluded to this in a message to reporters following the initial breach on July 31:

Hi to all mankind. The greatest leak of cyber space era is happening. What’s its name? Oh I forget to tell. Its HBO and Game of Thrones……!!!!!! You are lucky to be the first pioneers to witness and download the leak. Enjoy it & spread the words. Whoever spreads well, we will have an interview with him. HBO is falling.

Game of Thrones is the only series called out by name in this warning. Given the huge ratings and hype surrounding the show, the hackers may view targeting it as key to achieving their ends.