The episode was available on-demand to subscribers in Spanish and Nordic territories for one hour before being removed - long enough for it to be ripped and shared.
Footage from the episode was posted on Reddit (we won't link to the thread as it's full of spoilers) via YouTube, Instagram, Twitch and other streaming services, before swiftly being taken down.
At the time of writing, the full episode has just started being posted on torrent sites and is being uploaded with the file name 'Game_of_Thrones_-_S07E06.flv' to sites like Mega.nz faster than HBO can take the links down. The Independent can confirm it is real (and HD).
HBO Europe said in a statement (via AP) it had “learned that the upcoming episode of Game of Thrones was accidentally posted for a brief time on the HBO Nordic and HBO Espana platforms.
“The error appears to have originated with a third party vendor and the episode was removed as soon as it was recognized,” it added.
This is actually not the first time this has happened - an episode of season 6 having been accidentally uploaded by HBO's Nordic arm a few hours before official broadcast.
What with the HBO hack and the Indian leak of episode 4, Game of Thrones has had a rough season with spoilers, though it hasn't harmed ratings, with episodes posting recording viewing figures even when they've hit the web early.
This error is particularly egregious however given the importance of the episode, the penultimate instalment of season 7 seeing King Jon and his motley crew head north of the Wall to attempt to capture a White Walker.
Game of Thrones is broadcast on HBO, Sky Atlantic and through NOWTV on Sunday nights.
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