Unidentified "IT professionals" who recently hacked Home Box Office (HBO) have released a second batch of stolen data and demanded a ransom worth millions of U.S. dollars from the entertainment giant in order to prevent further leaks.

The latest data dump from HBO includes a month emails from one of the company's executives, series screenshots, financial balance sheets, marketing-strategy PDFs and a detailed script of the upcoming 5th episode of "Game of Thrones" Season 7, set to be aired next week, all watermarked with "HBO is Falling."

The hackers reportedly sent a video message, named "First Letter", published by Mashable on Tuesday, to HBO President and CEO Richard Plepler and demanded Bitcoins as a ransom for the stolen data otherwise the leaks would continue.

An individual calling themselves "Mr. Smith" said that "we have breached into your huge network," which "was one of our difficult targets to deal with but we succeeded."

"We want XXXX dollars to stop leaking your Data. HBO spends 12 million for Market Research and 5 million for GOT7 advertisements. So consider us another budget for your advertisements!" the video shows.

The hackers, who claimed to be "IT professionals," said they "often launch two major operations in a year and our annual income is about 12-15 million dollars."

That means the ransom may worth about 6 million dollars. The video letter offers HBO three days to pay the ransom.

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 on July 31th.

HBO, owned by media giant Time Warner Inc., released a statement, saying "HBO recently experienced a cyber incident, which resulted in the compromise of proprietary information."

However, the company did not confirm how much data the hackers have stolen.

An HBO spokesperson sent Mashable a statement on Tuesday in response to the video, saying "HBO believed that further leaks might emerge from this cyber incident when we confirmed it last week."

"While it has been reported that a number of emails have been made public, the review to date has not given us a reason to believe that our e-mail system as a whole has been compromised," the company said.

The company said they "continue to work around the clock with outside cybersecurity firms and law enforcement to resolve the incident."

The hackers anonymously emailed several reporters about the hack on July 30, saying "the greatest leak of the 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," 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 being 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."