Game of Thrones -- FAIL ... 4 Unaired Episodes LEAKED

There has been an epic breach on one of the most popular and successful shows on TV ... 4 of the 10 Season 5 episodes of "Game of Thrones" have been leaked ... and the downloading is predictably insane.

The timing is awful ... Season 5 kicks off tonight. It looks like someone took a DVD that was sent to the media for previews, blurred the watermark and posted it on several torrent sites.

As for the number of illegal downloads ... TorrentFreak claims in just 3 hours it was the beneficiary of more than 100,000 downloads.

HBO just issued a statement, acknowledging the leak vowing to actively figure out how it happened.

"Game of Thrones" is the most pirated TV show out there ... and this ain't gonna help.