Editor's note: The following review is about pornography. If the subject itself offends, please stop reading. Why write about it? First, because pornography is "intimately linked with the evolution of communications technology," as one history professor interviewed puts it. Second, because the porn industry, like the music and newspaper industries, faces a technological problem and doesn't know what to do next.

I was 29 and had been living in Los Angeles for nine months when I took a job with Larry Flynt Publications. Technology was the last thing on my mind, but that would change quickly. The most famous of the 20 magazines under the roof was Hustler, the raunchiest of the three big American skin mags. But within a year of my arrival, in 2000, some of the less popular titles folded, and it was clear that a shift was in the air.

The shift worked to my benefit--my bosses created an online division and put me in charge of its editorial side. From that perch I saw firsthand how changing technologies both benefited and wounded the mighty porn machine. When I joined Flynt, it produced 20 magazines and four websites; today, it produces a handful of magazines and dozens of websites. Smaller companies gained power, since it was cheaper to put material online than to package and distribute magazines, tapes, or DVDs. And in the most wide-reaching development, high-speed Internet has spawned something called tube sites--file-hosting sites that offer rivers of free streaming video. These sites threaten to undo porn as we've known it.

The troubles for the porn studios began with a technology called BitTorrent, introduced in 2001, which made it easy for people to share data files over the Internet. This technology provided the world with unlimited free music, much to the dismay of the giant music publishers. But it was still somewhat clunky. If you wanted to watch a video, you had to download it, which took time and ate up space on your hard drive.

By 2005, the BitTorrent technology gave way to something more manageable and user-friendly: streaming video. This technology was used early and heavily by sites with names like PornHub, Xvideos, and YouPorn. Suddenly, anybody who wanted to watch a clip could do so almost instantly. You clicked on a video and it played in the browser: no more waiting, no more downloading.

This simple innovation has demolished the porn industry's traditional way of doing business. Porn tube sites are now among the most visited websites in the world. According to the online measurement company Alexa, PornHub holds a worldwide traffic rank of 54. Xvideos is at number 53, and ­YouPorn is at number 64. The threat comes from the sheer ease of uploading content--anyone's content--onto a site and then drawing users to view it. Most tubes describe themselves as aggregators of "user-generated content," but the material they publish is much broader--many video clips are created, paid for, and owned by porn studios.

"Piracy has hurt us a lot," says Ali Joone, founder and director of the adult-film company Digital Playground, which last year tracked illegal downloads of its most popular title, Pirates. "Over the course of a month, it was downloaded about four million times. And that's just from a handful of sites. Even if those downloads cost us a thousand customers, let's say, who were going to pay--that hurts."

The porn studios face the same fundamental question as any content provider in the Internet age: how do you protect your stuff once it's "out there"? The answer, so far, is, "Not well."

The tube effect has been profound enough to inspire a recent public-service announcement featuring more than a dozen adult performers and directors pleading with fans not to view pirated porn. One actress, Charley Chase (who did not participate in the PSA but says she faces the same troubles), got into the business in late 2007 on the promise of lots of work at high pay. But the pay has dropped and the work has dried up. "And it's all because of piracy," she says.

According to Travis Nestor, a former agent for and a founder of the now-defunct It Models, a scene that might have paid an actress $900 in 2004 will now net her $600. In the same period, rates for male performers have dropped from around $500 per scene to $300. But that's only half the effect, because there are fewer studios making fewer movies. Joone says that five years ago the industry might have released 400 new titles a week, but that output has been cut in half. "People just aren't buying," he says.

It's difficult even for people in the industry to get a sense of how many studios have closed, partly because the porn business--unlike, say, the music business--does not consist of large conglomerates. Instead, it's made up of shifting constellations of modest-­sized companies. Diane Duke, executive director of the Free Speech Coalition, a trade association for the adult entertainment industry, says the number of studios is still in the thousands (representing everything from big production houses to "mom-and-pop shops"), but it's dropping. "Our industry is woefully lacking in stats," she says. "Everybody keeps their numbers tight to their chest. But we've definitely seen the decline."

The tube sites, meanwhile, find shelter in the Digital Millennium Copyright Act, a U.S. law passed in 1998. The act says that websites aren't responsible for any copyrighted material that shows up on their pages unless somebody points it out to them. "But that only protects them up to the point that they receive a cease-and-desist letter from us," says Joone. "Then they have to take it down. If they don't take it down, then that's copyright infringement."