'X-Men Origins: Wolverine' leaked online

"X-Men Origins: Wolverine” isn’t due in theaters until next month, but the prequel has already hacked its way online.A high-quality, full-length work print of the 20th Century Fox film, which is set for release May 1, appeared online Tuesday. The film focuses on the beginnings of Hugh Jackman’s clawed Marvel superhero Wolverine.

Someone stole an "incomplete and early version" of the next installment in the blockbuster X-Men movie series and posted it on the Internet this week, according to the studio that owns the billion-dollar film franchise.

Twentieth Century Fox said the FBI was investigating who leaked "X-Men Origins: Wolverine," which is set for release in U.S. theaters May 1.

"The source of the initial leak and any subsequent postings will be prosecuted to the fullest extent of the law; the courts have handed down significant criminal sentences for such acts in the past," the studio's statement said.

Removing the pirated files from the Internet may prove an impossible challenge, an industry source said. This source did not want to be named because of the sensitive nature of the matter.

Although the studio said it was removed from the Web site that first hosted it, the digital file has probably been downloaded tens of thousands of times, the source said.

"It's not removed from the Internet," the industry source said. "It's still there."

Twentieth Century Fox downplayed the value of the pirated copy, noting that it was not the final version.

"It was without many effects, had missing and unedited scenes and temporary sound and music," the studio said.

Investigators have several tools to help find the source of the leak, including digital watermarking, the studio said.

"We forensically mark our content so we can identify sources that make it available or download it," the studio said.

An FBI spokeswoman confirmed that the agency is "working with the studio and investigating the alleged online compromise of the movie."

The Motion Picture Association of America, the film industry's main trade association, confirmed it was also helping in the probe.

Whether the leaked video will eventually hurt the film's box office earnings "is very difficult to discern," the industry source said