Euron Greyjoy isn't the only pirate that HBO's Game of Thrones has to worry about now.

Entertainment Weekly reports that hackers have breached the cable network's systems, and claim to hav obtained 1.5 terabytes of data, including upcoming episodes of both Ballers and Room 104, which have already been leaked online. The group's reported crown jewel, however, is unspecified written material from the next episode of Game of Thrones.

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"HBO recently experienced a cyber incident, which resulted in the compromise of proprietary information,” the network confirmed in a statement. “We immediately began investigating the incident and are working with law enforcement and outside cybersecurity firms. Data protection is a top priority at HBO, and we take seriously our responsibility to protect the data we hold."

The statement was released after an anonymous email from the alleged hacker group went out to several reporters on Sunday, stating, "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."

It is unclear whether the group has obtained full episodes of the fantasy drama's penultimate season, but if so, it wouldn't be the first time that Game of Thrones has been leaked. The first four episodes of the fifth season were released online before that season had even premiered, leading to HBO to stop sending out advance copies for review by journalists.

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Piracy is becoming an increasingly prevalent issue for Hollywood. Disney received a ransom demand in May from hackers who threatened to leak a film believed to be Pirates of the Caribbean: Dead Men Tell No Tales, and several episodes of Netflix's Orange Is the New Black Season 5 were released ahead of the official premiere.

Game of Thrones‘ seventh season airs Sunday at 9 p.m. ET/PT on HBO. Based on George R.R. Martin's bestselling fantasy series A Song of Ice and Fire, the hit drama stars Peter Dinklage as Tyrion Lannister, Nikolaj Coster-Waldau as Jaime Lannister, Lena Headey as Cersei Lannister, Emilia Clarke as Daenerys Targaryen and Kit Harington as Jon Snow.