Group tells company CEO to pay multimillion-dollar ransom or else risk 1.5TB of shows and confidential corporate data being released online

Hackers of US television network HBO have released personal phone numbers of Game of Thrones actors, emails and scripts in the latest dump of data stolen from the company, and are demanding a multimillion-dollar ransom to prevent the release of whole TV shows and further emails.

In a five-minute video letter from somebody calling themselves “Mr Smith” to HBO chief executive Richard Plepler, the hackers told the company to pay within three days or they would put online the HBO shows and confidential corporate data they claim to have stolen.

The hackers claim to have taken 1.5TB of data – the equivalent to several TV series box sets or millions of documents – but HBO said that it doesn’t believe its email system as a whole has been compromised, although it did acknowledge the theft of “proprietary information”.

HBO said it is continuing to investigate and is working with police and cybersecurity experts.

The hackers demanded “our six-month salary in bitcoin”, claiming they earn $12m to $15m a year from blackmailing organisations whose networks they have breached. They said they would only deal directly with “Richard” and only send one “letter” detailing how to pay.

Along with the video, the hackers released 3.4GB of files. The dump contained technical data detailing HBO’s internal network and administrator passwords, draft scripts from five Game of Thrones episodes, including this week’s instalment, and a month’s worth of emails from HBO’s vice president for film programming, Leslie Cohen.

The hackers claim it took six months to break into HBO’s network, and that they spend $500,000 a year purchasing so called zero-day exploits that let them break into networks through holes not yet known to Microsoft and other software companies.

Many of the more than 50 internal documents released were labelled “confidential”, including a spreadsheet of legal claims against the TV network, job offer letters to several top executives, slides discussing future technology plans, and a list of 37,977 emails called “Richard’s Contact list”, an apparent reference to Plepler.

One document appears to contain the confidential cast list for Game of Thrones, listing personal telephone numbers and email addresses for actors such as Peter Dinklage, Lena Headey and Emilia Clark.

The HBO leaks have been limited so far, falling well short of the chaos inflicted on Sony in 2014 when North Korea-linked hackers broke in and stole troves of data, including embarrassing emails and the personal details of employees. The hackers’ biggest threat appears to be dumping videos of future shows online with their logo “HBO Is Falling” superimposed. They claim that HBO is their 17th target and that only three of their past targets have refused to pay.