HBO has reportedly been the victim of a cyberattack, with an unknown hacker claiming to have scripts from its flagship show Game of Thrones and "1.5 terabytes of data" pilfered from the firm's computer networks, Entertainment Weekly reported this week (Monday 31 July).

"HBO recently experienced a cyber incident, which resulted in the compromise of proprietary information," a spokesperson for the network said. "We immediately began investigating the incident and are working with law enforcement and outside cybersecurity firms."

The company said data protection remained a "priority".

Entertainment Weekly said episodes of TV shows Ballers and Room 104 had already been leaked online alongside a script for an unreleased Game of Throne episode. The hacker said that more releases of HBO material would be "coming soon".

No individual GoT episodes have leaked so far.

The firm's CEO Richard Plepler told staff via email there had been a "cyber incident directed at the company", but did not elaborate on what exactly had been stolen.

"Any intrusion of this nature is obviously disruptive, unsettling, and disturbing for all of us," he wrote.

The email added: "I can assure you that our senior leadership and our extraordinary technology team, along with outside experts, are working round the clock to protect our collective interests. The problem before us is unfortunately all 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."

A notice sent to reporters from the alleged hacker concluded with the warning that "HBO is falling".

Back in April, a hacker using the name The Dark Overlord leaked unaired episodes from Netflix show "Orange is the New Black" after failing to extort a studio for tens of thousands of dollars.

The same hacker later teased a Disney hack, but that was declared a hoax.

"To our knowledge we were not hacked," Disney chief Bob Iger said at the time. "We had a threat of a hack of a movie being stolen. We decided to take it seriously but not react in the manner in which the person who was threatening us had required.

"We don't believe that it was real and nothing has happened."

The Dark Overlord has been linked to a number of cyberattacks against healthcare facilities in the US, often threatening to release private information if a ransom is not paid. It remains unknown if the pseudonym is linked to an individual or a collective working to extort victims.