NYTimes.com

Hollywood may at last be having its Napster moment — struggling against the video version of the digital looting that capsized the music business. Media companies say that piracy — some prefer to call it “digital theft” to emphasize the criminal nature of the act — is an increasingly mainstream pursuit. At the same time, DVD sales, a huge source of revenue for film studios, are sagging. In 2008, DVD shipments dropped to their lowest levels in five years. Executives worry that the economic downturn will persuade more users to watch stolen shows and movies.

TorrentFreak.com, a Web site based in Germany that tracks which shows are most downloaded, estimates that each episode of “Heroes,” a series on NBC, is downloaded five million times, representing a substantial loss for the network. (On TV, “Heroes” averages 10 million American viewers each week).

But if media companies are winning the battle against illegal video clips, they are losing the battle over illicit copies of full-length TV episodes and films. The Motion Picture Association of America says that illegal downloads and streams are now responsible for about 40 percent of the revenue the industry loses annually as a result of piracy.

“It is becoming, among some demographics, a very mainstream behavior,” said Eric Garland, the chief executive of BigChampagne.