The company said it was working with police and cyber security experts after the incident. The hacking attack resulted in the theft of over a terabyte of HBO's data, the hacker group responsible for the attack is claiming.
The incident could mean that the upcoming episodes of Game Of Thrones' current, seventh season could leak online ahead of schedule. According to the website, an anonymous email was set to many reporters earlier today announcing the hack.
Hi to all mankind. What's its name? Oh I fort to tell.
Watch out, Game of Thrones fans, because it looks like HBO has suffered a data breach, putting information about upcoming episodes of the show out in the open. It also promised an interview opportunity to journalists who spread word of the attack.
"Any intrusion of this nature is obviously disruptive, unsettling, and disturbing for all of us", said HBO CEO Richard Pepler.
HBO did not reveal what data had been stolen or posted online, and there was no indication of whether the breach included customer data or personal information about employees.
This isn't the first time Game of Thrones has experienced a leak.
The penultimate season of the global smash hit has already enjoyed record-breaking ratings, with the first episode drawing an impressive 10.1 million viewers.