In an email to HBO staff Wednesday, CEO Richard Plepler said the company's email system likely was not affected in Monday's hacking of the cable network.
"We do not believe that our email system as a whole has been compromised," Plepler wrote, warning his staff to be wary of media speculation about the breach.
A script outline for the next episode of Game of Thrones, along with episodes of Ballers, Barry and Room 104, were published online Monday.
A company called IP Echelon reportedly submitted a request to Google on behalf of HBO to take down the leaked material.
HBO has not publicly commented on specifically what material has been hacked, but the request claimed that "thousands of Home Box Office [HBO] internal company documents" had been leaked in addition to the video content.
According to Variety, the initial leak was much larger than first reported, and personal information about one senior HBO executive, as well as access information to dozens of online accounts, have been published since Monday.
The hackers, who claimed to have accessed 1.5 terabytes of information,
said more is coming.
If the claim is true, it would make this hack even larger than the crippling cyberattack on Sony in 2014, which the FBI has blamed on the North Korean government. North Korea denied the allegation.