The hackers proceeded to leak unreleased episodes of a handful of shows, and promised to leak more data in the coming days.

If the hacker's claims are true and 1.5 terabytes of data was stolen from HBO, the breach would be considerably bigger than the amount of data published after the Sony Pictures hack in 2014, when 200 gigabytes of data was leaked online.

With popular series like Game of Thrones, HBO has struggled to prevent piracy.

HBO began an internal forensic investigation immediately after the hack occurred, led by the F.B.I. and cybersecurity firm Mandiant.

The Reports revealed that the supposedly hijacked Game of Thrones script emerge from the fourth episode of (season 7), which presently is being televised.

CEO Richard Plepler has that said some of the stolen material included some of HBO's programming, though he has not identified which programming.

Word of HBO getting hacked first broke Monday morning, when the hackers approached media outlets with the news that they had broken into HBO's networks and released episodes of "Ballers", "Insecure," and "Room 104" as well as the script for an upcoming episode of "Game of Thrones".

The breach exposed embarrassing email exchanges between high-powered actors and executives, cost the studio tens of millions of dollars and top executive Amy Pascal lost her job.

Purported said in email that they'd accessed HBO's and system and then posted stolen information online. By comparison, the print content stored in the Library of Congress is around 10 terabytes.

The hack comes at a sensitive time for HBO, as its parent Time Warner Inc is waiting for regulatory approval to sell itself to AT&T Inc in an $85.4 billion deal announced in October.