U.S. cable network HBO has recently suffered a major cyberattack, causing the upcoming episodes of its biggest series "Game of Thrones" to be stolen and leaked online.

The hackers, who broke into the company's system, claimed to have grabbed 1.5 terabytes of HBO data, including a script for an upcoming episode of "Game of Thrones," and videos of new episodes of shows such as "Ballers" and "Room 104," according to Entertainment Weekly. The cybercriminals threatened that more is to come.

HBO confirmed the cyber-incident that resulted in "compromise of proprietary information," according to a company statement on Monday. "We immediately began investigating the incident and are working with law enforcement and outside cybersecurity firms. Data protection is a top priority at HBO, and we take seriously our responsibility to protect the data we hold."

It still remains unknown how the hackers breached HBO's system, how much data they robbed and whether there was a ransom.

HBO is the latest among a line of Hollywood companies that have long been targeted by cybercriminals. In May, Walt Disney was held to ransom as hackers threatened to expose "Pirates of the Caribbean 5" before its official release. But Disney chief Bob Iger later scorned the threat as a hoax.