Ethan explains to me that the Christmastime break-in didn't proceed very far. While logged into MediaDefender on one computer, he chatted on another with some hacker friends to see if they knew anything about the firm. But the conversation quickly shifted to other exploits the group wanted to pull off on that cold evening—cell-phone hacks, fake pizza deliveries, denial-of-service attacks—and Ethan moved on.

In the spring, however, he decided to explore the company again. Over the next few months, Ethan says, he figured out how to read MediaDefender's email, listen to its phone calls, and access just about any of the company's computers he wanted to browse. He uncovered the salaries of the top engineers as well as names and contact information kept by C.E.O. and co-founder Randy Saaf (with notations of who in the videogame industry is an "asshole" and which venture capitalists didn't come through with financing). Ethan also figured out how the firm's pirate-fighting software works. He passed on his expertise to a fellow hacker, who broke into one of MediaDefender's servers and commandeered it so that it could be used for denial-of-service attacks.

Ethan continued to log in to MediaDefender about twice a week throughout the summer of 2007. Usually, he'd head down to the basement office after his S.A.T. prep classes. After a while, his friends grew tired of hearing about his stunts inside Monkey Defenders, as he began to call the company. And eventually, he himself got bored. So in September, he decided to give the entire thing up, but not before he and a few fellow hackers pulled a prank: They grabbed a half-year's worth of internal emails and published them on the same file-sharing sites prowled by MediaDefender. A comment posted with the messages read, "By releasing these emails we hope to secure the privacy and personal integrity of all peer-to-peer users. The emails contains [sic] information about the various tactics and technical solutions for tracking P2P users, and disrupt P2P services.... We hope this is enough to create a viable defense to the tactics used by these companies." It was signed MediaDefender-Defenders.

A few days later, Ethan and his friends put more material online. One file contained the source code for MediaDefender's antipiracy system. Another demonstrated just how deep inside the company they had gone. This file featured a tense 30-minute phone call between employees of MediaDefender and the New York State attorney general's office discussing an investigation into child porn that the firm was assisting with. (MediaDefender refused to comment for this story.) The phone call makes clear that the hackers had left a few footprints while prowling MediaDefender's computers. The government officials had detected someone trying to access one of its servers, and the hacker seemed to know all the right log-in information. "How comfortable are you guys that your email server is free of, uh, other eyes?" an investigator with the attorney general asked during the call.

"Oh, yeah, yeah, we've checked out our email server, and our email server itself has not been compromised," the MediaDefender executive said.

But, of course, it had.

"In the beginning, I had no motivation against Monkey Defenders," Ethan tells me. "It wasn't like, 'I want to hack those bastards.' But then I found something, and the good nature in me said, These guys are not right. I'm going to destroy them."

And so he set out to do just that: a teenager, operating on a dated computer, taking on—when his schedule allowed—one of the entertainment world's best technological defenses against downloading. The U.S. movie industry estimates that it loses more than $2 billion a year to file sharers; the record industry, another $3.7 billion. "Piracy," intoned Dan Glickman, the head of the Motion Picture Association of America trade group, to Congress in late 2006, "is the greatest obstacle the film industry currently faces." Instead of figuring out whether there is a way to make online distribution work—to profit from downloading—the industry has obsessed for years with battling it. Yet it took only a few months for Ethan to expose just how quixotic that fight has become.