After its fifth season began Sunday, users of a Twitter-owned live-streaming app shared the fantasy drama.
HBO said Tuesday it sent "take down notices" to Periscope, the app that allows video streaming from users' phones to their Twitter followers.
Twitter, which recently acquired Periscope, said the app complies with U.S. copyright law and responds to valid take-down requests.
On Monday, HBO said four unaired "Game of Thrones" episodes that were leaked online had come from within a group authorized to receive preview DVDs.
The unrelated incidents don't appear to have hurt the show's ratings. HBO hasn't released figures, but reports say nearly 8 million viewers tuned in to the premiere, the series' best start yet.