LOS ANGELES -- Unidentified Hackers have issued a threat to release additional stolen contents days after leaking unaired episodes of the entertainment giant Home Box Office (HBO) in Hollywood.

The hackers said in an automated email that it will "release the leaks gradually every week," with the next release coming "Sunday 12 GMT," a roll-out that echoes HBO's own original programming schedule.

The hackers claimed to have stolen 1.5 terabytes of data from HBO and promised more leaks after releasing a script for the upcoming episode "Game of Thrones" Season 7 as well as videos of unaired shows such as "Ballers" and "Room 104", Entertainment Weekly reported Monday.

HBO, owned by media giant Time Warner Inc., later confirmed the cyber attack on its network and released a statement, saying "HBO recently experienced a cyber incident, which resulted in the compromise of proprietary information."

The company said it "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 anonymously emailed several reporters about the hack on Sunday, saying "the greatest leak of cyber space era is happening," according to Entertainment Weekly.

"The problem before us is unfortunately 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," HBO's chairman and CEO Richard Plepler said.

For years, the entertainment company has been fighting hard to prevent "Game of Thrones" storylines from leaking. In 2015, the first four episodes of Season 5 were leaked online before aired.

However, HBO is not the only target of cybercriminals. Netflix was attacked in April by a hacker, who uploaded episodes of the new season of "Orange Is the New Black."

The biggest Hollywood hack victim has been Sony Pictures Entertainment, whose approximately 100 terabytes of data were uploaded online in 2014, when it was about to release a fictional comedy about attempting to assassinate the leader of the Democratic People's Republic of Korea Kim Jong-un.