London: The hackers who leaked unaired episodes of HBO's shows, including 'Game of Thrones', earlier this week have now threatened to release additional content on Sunday. The hacker group wrote in an automated email reply sent to Variety.com, that it will release the leak gradually every week and added that the next release may come this Sunday at 12 GMT (5 p.m. IST). The group also repeated its claim that it had obtained a total of 1.5TB of data when it broke into HBO's computer networks, Variety.com reported on Friday. Russian cyber security firm Kaspersky Lab termed the incident a new phenomenon as far as cyber crimes go. "The HBO attack was relatively a new phenomenon. At first and throughout the 90s and early 2000s, most hackers intended primarily on vandalism attacks rather than for making money. But with time, it became clear that cyber attacks could bring with them serious money," Altaf Halde, MD, Kaspersky Lab, told IANS. "The value of such a cyber hack is entirely dependent on how much attention it can bring. Hacking into HBO and stealing 'Game of Thrones' piggybacks on one of the most active talking points in the world. Entertainment companies are like governments and hacking groups in that their intellectual property is of interest to everyone," Halde added. There were fears among HBO's employees of their personal data having been accessed by the hackers, but the company denied the notion. "At this time, we do not believe that our email system as a whole has been compromised, but the forensic review is ongoing," Richard Plepler, President and CEO, HBO, said earlier this week. However, according to Variety.com, a security contractor hired by HBO to scrub search results for the leaked data from Google revealed in a filing on Tuesday that the hackers got their hands on "thousands of internal documents". The hacker group on Monday had leaked 1.5TB of HBO's data including the script of the next episode of 'Game of Thrones' and unreleased episodes of 'Ballers' and 'Room 104' -- two of HBO's other shows, after which the TV network started an investigation in the matter.