WASHINGTON: Already the most pirated show in television history, HBO's fantasy epic Games of Thrones was hit by a new leak Sunday just hours before the premiere of its hotly-anticipated fifth season.

With the start of the new series due to air simultaneously at 0100 GMT Monday in 170 countries, eager but unscrupulous fans were already downloading four leaked episodes.

“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. We're actively assessing how this breach occurred,” the cable TV network said.

HBO had decided on the unusual simultaneous global release schedule because the series' fervent following has made it a hot property.

The 2014 season was illegally downloaded more than eight million times, making it the most pirated show in the world for the fourth year running, according to specialist news site TorrentFreak.

Based on American novelist George R.R. Martin's fantasy series “A Song of Ice and Fire,” the saga is a feast of blood, sex and betrayal.

It recounts the implacable fight for power among several families in an imaginary landscape of kingdoms and continents inspired by the history of the Middle Ages