HBO has been hit with a cyberattack, resulting in upcoming episodes of at least two HBO series being leaked online along with written material from next week’s fourth installment of the current season of “Game of Thrones,” EW.com reports.

HBO confirmed the attack, releasing a statement saying: “HBO recently experienced a cyber incident, which resulted in the compromise of proprietary information. 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 hackers claim to have gathered 1.5 terabytes of material, EW reports, noting that upcoming episodes of “Ballers” and “Room 104” have apparently been released online, with the hackers vowing that more is on the way.

HBO Chairman and CEO Richard Plepler discussed the attack in an email circulated to HBO employees in which he again noted the efforts by the company to investigate the situation. He added: “The problem before us is unfortunately all too familiar in the world we now find ourselves a part of. As has been the case with any challenge we have ever faced, I have absolutely no doubt that we will navigate our way through this successfully.”

EW notes that a number of reporters received an anonymous email on Sunday announcing the attack. The report quotes the email saying: “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.”

The report notes that no “Game of Thrones” episodes have yet been leaked.