With just days to go before "Harry Potter & the Deathly Hallows: Part 1" premieres Friday, the first 36 minutes of the Warner Brothers release have started popping up on various bit torrent sites.
The studio said that it did not know how the pirated material got leaked online, but said it was working to find a culprit.
"This constitutes a serious breach of copyright violation and theft of Warner Bros. property. We are working actively to restrict and/or remove copies that may be available. Also, we are vigorously investigating this matter and will prosecute those involved to the full extent of the law," Warner Brothers said in a statement.
"Potter" films are popular with online pirates. The most recent installment ranked among the top 10 most pirated films of 2009 with 7.9 million illegal downloads.