Warning: If you don't want to learn any of the plot twists to this summer's blockbusters, don't read any further.

Even before the opening credits scroll across the screen, some theatergoers will know how the movie ends, who the real villain is and which hero gets his head lopped off. And the Web sites that reveal these "spoilers" before movies are out have fans and studios hopping mad.

"I'm trying to avoid them quite actively, but if you go to any movie site, it's amazing how much leaks," movie fan Bill Robertson said in a phone interview from London. "Before Phantom Menace, I went to a Web site I assumed would be spoiler-free, and it said Darth Maul gets cut in half. It deflated the movie for me."

Indianapolis information-technology specialist Rolf Crozier, 36, put the blame on Web sites like aintitcoolnews.com and filmjerk.com.

"I like to be surprised! I like to be entertained! I'm not some 4-year-old who can't wait for Christmas and wants to open my presents two weeks before!" he wrote in an e-mail. "Those mindless idiots who post major spoilers are just friendless movie geeks begging for attention!"

And studios have to deal with the downside of leaks. Bad word-of-mouth can deter audiences before a picture has even finished production, said Robertson, 32, who is a PR manager for a company that handles British publicity for Mission Impossible and Star Wars.

"People get disillusioned before they even go see a movie," he said. "A lot of sites have a tendency to say, 'Don't go see this film, De Niro only pops in for 15 minutes.' American Beauty was an example of that. If you know Kevin Spacey dies at the end, you'd think beforehand that this movie is going to be really downbeat, just rubbish. But it's actually a movie that's quite life-affirming."

But audiences get the tidbits they crave, and studios — no matter how much they protest — benefit from the gossip, according to Scott Chitwood, co-editor of theforce.net, which specializes in Star Wars scoops.

"It's a bit of a love-hate relationship," he said. "We keep the excitement of the movies going in the time between the movies, but at the same time we leak things they don't want leaked."

"It's probably more hate now than love," he added after a moment's reflection.

The studios contacted for this story either did not respond, or chose not to comment.

Using sources who can be surprisingly close to the upper echelons of a movie production, spoiler sites can basically tell you anything about an upcoming flick.

"One day I had the janitor and the head of production send me the same scoop about the same movie," said Garth Franklin, who runs darkhorizons.com.

Franklin said he avoids spoilers as much as he can. Instead of revealing endings, darkhorizons.com offers pithy reports on casting, costume design and the broad strokes of the plot.

But Franklin acknowledged that "spoiler" doesn't mean the same thing to everyone. Once he got flak for publishing a photo of the costume Ben Affleck wears in Daredevil.

"Some would say that's a spoiler, but that's going to be spoiled in the first trailer anyway," he said.

And that's the irony, according to IGN FilmForce editor-in-chief Brian Zoromski. Though spoiler sites get criticized for spilling the beans, moviegoers learn more movie secrets from mainstream sources, he said.

"I think people can be a lot more spoiled for a movie if they just read the industry trades like Hollywood Reporter and Variety because they will nonchalantly give away major details, like saying so-and-so plays the killer in a movie that isn't a thriller until the end," Zoromski said.

FilmForce, on the other hand, includes warnings before each spoiler, he pointed out.

Sometimes spoilers can even come in official merchandise, like — and here comes a spoiler — the picture of Anakin Skywalker's severed arm in the book companion to Attack of the Clones, Chitwood said.

But for the most part, spoiler sites say they hear more compliments than complaints, if only because those who don't want to know a film's secrets can simply stay away.

Well, most of them.

"It's like a drug, or like a train wreck, actually; you can't not look when you know it's there," 29-year-old marketer Mary Gorman wrote in an e-mail. "It feels cool to be in the know, to know what's going on before anyone else. At the same moment, though, the base enjoyment you get from films, the element of surprise for which we pay our $9 admission, is ruined."