The Justice Department announced yesterday that it had seized a Web site dedicated to online copyright infringement that is used by tens of thousands of people every day -- the first time the government has taken a domain name in a criminal piracy case.

The takeover of the site, www.isonews.com, came as part of a plea agreement involving David M. Rocci of Blacksburg, Va., who ran the site and who pleaded guilty in U.S. District Court in Alexandria to violating federal copyright laws.

Officials described the site, with more than 100,000 regular users and more than 140,000 hits each day, as the nation's leading public Internet site dedicated to online computer piracy. The officials plan to post information about the criminal case against Rocci and about copyright infringement on the Web site, along with links to Justice Department sites.

Rocci, 22, who used the online screen name "krazy8," pleaded guilty Dec. 19 to one count of conspiracy to violate the Digital Millennium Copyright Act by trafficking in devices known as modification, or "mod," chips. Those are computer chips used to circumvent copyright protections in such game systems at Playstation2 and XBox, allowing users to illegally play pirated sports, racing and other games on their televisions.

Prosecutors said Rocci used the Web site to market and advertise the sale of these chips, selling about 450 of them in the United States and overseas for two months starting in May 2002. He made about $28,000.

Because the Web site was "facilitating" the crime and because Justice Department officials wanted to send a message to other violators, they came up with the idea of seizing the site. Officials said this could be a harbinger of enforcement actions.

"Piracy is not a game or a hobby; it is a crime," Paul J. McNulty, the U.S. attorney in Alexandria, said in a statement. "Whether you are engaged in conduct like David Rocci or you are purchasing mod chips to play pirated games, you should stop. As David Rocci and others have learned recently, the consequences of copyright infringement are very real."

McNulty's office prosecuted the case with the Justice Department's Computer Crime and Intellectual Property Section. Officials would not say what triggered the investigation, though they acknowledged having been aware of the site because of its wide usage. The investigation is ongoing, but officials would not say whether Rocci's guilty plea means he is cooperating or whether others could face charges.

Rocci faces up to five years in prison and a $500,000 fine when he is sentenced on March 7. As for the future of his site, Justice Department officials said they intend to leave their messages on it for a number of days. It is unclear whether the site will be shut after that.

Rocci and his attorney did not return telephone calls.