WASHINGTON (AFP) - Hackers claiming to have breached HBO were demanding millions of dollars in ransom payments from the television group, while threatening to release more files from what is claimed to be a massive data breach.

A video circulating online directs a message to HBO chief Richard Plepler claiming that the group "obtained valuable information" in an attack that yielded a whopping 1.5 terabytes of data.

The message was authored by someone identified only as "Mr. Smith."

The website Databreaches.net reported that 10 files were leaked Monday as part of the demand including what may be another script of the popular fantasy series Game Of Thrones.

The video revealed a letter stating the hackers obtained "highly confidential" documents and data including scripts, contracts and personnel files.

"We want XXX dollars to stop leaking your data," the letter said, later alluding to a figure of half the group's annual budget of US$12 million to US$15 million (S$16 million to S$20 million) .

It went on to say, "HBO spends 12 million for Market Research and 5 million for GOT7 advertisements. So consider us another budget for your advertisements!"

The message comes a week after a leak of one script of Games Of Thrones" and content from other productions.

The letter said HBO was the 17th target for the hacking group and that "only 3 of our past targets refused to pay and were punished very badly and 2 of them collapsed entirely."

HBO said in a statement that it believed that further leaks might emerge from the breach and that "the forensic review is ongoing."

"While it has been reported that a number of e-mails 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 statement from the Time Warner unit said.

"We continue to work around the clock with outside cybersecurity firms and law enforcement to resolve the incident."