Last summer's first two blockbuster films, Spider-Man and Star Wars: Episode II-Attack of the Clones, played on more than 3,000 movie screens and grossed more than $100 million in their opening weeks. Impressive numbers. But not as impressive as the numbers generated by these movies' actual opening nights.

A bootlegged copy of Spider-Man appeared on the Internet the day before the movie premiered in theaters. A copy of Attack of the Clones-as if to mock its title-was widely available a week before that movie's scheduled release. From that virtual opening, which was accessible to half a billion people on their home computers, its Hollywood producers grossed exactly $0.

Many bootlegged movies are "cammers," shot by digital cameras that had been sneaked into movie-screening rooms. The better copies are shot illicitly with cameras placed on tripods in the projection booth. The best ones are produced directly from studio prints or DVDs. Hopelessly dingy or surprisingly good, most of the copies have one feature in common. They are released in a format called DivX, a digital video-compression technology that shrinks movies into packages small enough to be sent over the Internet or stored on standard compact discs.

These Internet premieres mark a milestone in the long-anticipated "Napsterization" of the movie industry. Just as music file-sharing software allowed Internet users to send millions of bootlegged music files freely over the Web, DivX threatens to do the same for full-length films. "Hollywood's worst nightmare has come true," says Robert Batchelder, a research director in new media at Gartner, a consulting firm based in Stamford, CT. "You used to need a factory to make quality copies of movies. Now you just buy a computer with a CD burner."