Hackers who leaked a trove of “Game of Thrones” episodes have threatened to leak footage – and the personal contact details of the show’s stars – unless they are paid a large ransom.

The anonymous group demanded around $7 million (£5.4 million) to stop them posting the information publicly.

They claim to have personal phone numbers and email addresses for Emilia Clarke, Peter Dinklage and Lena Headey, as well as more as-yet unreleased footage from the HBO series.

The threat was posted as alongside a 3.4 GB cache of other data allegedly stolen from HBO.

According to a report by the Associated Press, it contains:

    A detailed summary of an upcoming episode. One month's of email from the inbox of an HBO executive. A screenshot of folders, with labels like "Budgets," "Legal," and "Licensing & Retail." Documents containing the phone numbers and email addresses for cast members.

The demands came in the form of a five-minute video addressed to HBO CEO Richard Plepler from a "Mr. Smith," outlining the group's latest demands. According to WIRED, the video is set to the "Game of Thrones" theme music.

According to the AP, the letter was written in English "peppered with misspellings and pop-culture references."

The hackers said it took them six months to penetrate HBO's network, and phrased their demand for cash in terms of a "salary" for their efforts.

The video said they want their "6-month salary in bitcoin." The hackers said they usually make $12 million to $15 million a year from blackmail such as this. At that rate, six months of money would be between $6 million and $7.5 million.

The hackers gave HBO three days to deliver the payment, although their letter was not dated, the BBC noted.

On July 31, the group claimed to possess a total of 1.5 terabytes (1,500 GB) of data from the TV network.

The leakers' website - Winter-Leak.com - appears to be down. It is not immediately clear why.

An HBO spokesperson told The Hollywood Reporter that the company was conducting a "forensic review," and that it does not believe that its "e-mail system as a whole has been compromised."

The FBI and cybersecurity firm Mandiant, which investigated the 2014 Sony hack, are working with HBO to get to the bottom of the issue, THR reported.