Hackers using the name "Mr. Smith" have posted a fresh cache of stolen HBO files online, and demanded the network pay a ransom of several million dollars to prevent further such releases.

Key points: The hackers claim it took about six months to breach HBO's network

The hackers claim it took about six months to breach HBO's network The group say they earn at least $12 million to $15 million a year from blackmailing organisations

The group say they earn at least $12 million to $15 million a year from blackmailing organisations A fresh cache of stolen HBO files online has been posted online

The data dump included what appeared to be scripts from five Game of Thrones episodes, including one upcoming episode, and a month's worth of emails from the account of HBO's vice-president for film programming, Leslie Cohen.

There were also internal documents, including a report of legal claims against the network and job offer letters to top executives.

HBO, which previously acknowledged the theft of "proprietary information," said it was continuing to investigate and was working with police and cybersecurity experts.

The network has repeated its earlier assertion that it did not believe its entire email system had been compromised.

This is the second data dump from the purported hacker.

So far the HBO leaks have been limited, falling well short of the chaos inflicted on Sony in 2014.

In that attack, hackers unearthed thousands of embarrassing emails and released personal information, including salaries and social security numbers, of nearly 50,000 current and former Sony employees.

Those behind the HBO hack claimed to have more data, including scripts, upcoming episodes of HBO shows and movies, and information damaging to HBO.

In a swaggering five-minute video directed to HBO chief executive officer Richard Plepler, "Mr Smith" used white text on a black background to threaten further disclosures if HBO does not pay up.

In short — pay up within three days or the group, which claimed to have stolen 1.5 terabytes of HBO shows and confidential corporate data, would upload entire series and sensitive proprietary files.

The hackers claimed it took about six months to breach HBO's network.

Their biggest threat appears to be dumping videos of future shows online with their logo "HBO Is Falling" superimposed.

The hackers demanded "our 6-month salary in bitcoin," and claimed they earnt $12 million to $15 million a year from blackmailing organisations whose networks they had penetrated.

They said they would only deal directly with "Richard" and only send one "letter" detailing how to pay.

The dump itself was just 3.4 gigabytes, mostly technical data that appears to provide a topography of HBO's network and to list network-administrator passwords.

Many of the more than 50 internal documents in the dump were labelled "confidential," including a spreadsheet of legal claims against the 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 Mr Plepler.

One screenshot labelled "Highly Confidential" by the hackers listed folders such as "Penguin Random House," ''Licensing & Retail," ''Legal," ''International" and "Budgets".

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

The video letter uploaded claimed the hackers spend half a million dollars a year to purchase "zero-day" exploits that let them break into networks through holes not yet know to Microsoft and other software companies.

It claims HBO is the hackers' 17th target and that only three of their past targets refused to pay.

AP