Millions of people illegally downloaded pirated episodes from Season 5 of “Game of Thrones.” The first four episodes of the hugely popular HBO series leaked before its Sunday night premiere, leading to a piracy frenzy that will almost certainly continue thanks to the involvement of major torrent sites like EZTV.

More than 135,000 people were “seeding,” or hosting, video files containing Season 5, episode 1 of “Game of Thrones.” That episode had already been downloaded more than a million times, TorrentFreak reported, with metrics indicating that episodes 2-4 aren't far behind. The pirate files were most popular in Britain, followed by the United States, India, Canada and France, TorrentFreak reported.

Exactly how the first four episodes of such a closely guarded show leaked online before they were scheduled to air remains unclear, though the likeliest source is a journalist who was sent pre-premiere review copies. Initial doubts over whether the files were intentionally leaked as promotional bait by HBO subsided when well-known piracy providers like EZTV and ETTV made the files available.

“Sadly, it seems the leaked four episodes of the upcoming season of 'Game of Thrones' originated from within a group approved by HBO to receive them,” an HBO spokesperson told Mashable. “We're actively assessing how this breach occurred.”

The unaired episodes had been downloaded nearly 2 million times by Sunday morning, the piracy tracking company Excipio reported to Variety.

The creators of “Game of Thrones,” named the most pirated show of 2014, have tried to plug the leaks over the course of the production of Season 5.

“The cast is looping all over the world, sending files back and forth. Artists are working in special-effects houses all over the world,” Greg Spence, the producer in charge of post-production, told the Denver Post. “The files are watermarked, and editors have to confirm in writing that they're deleting them.”