In a series of raids in recent weeks, the Justice Department has extended such grabs to property that might seem esoteric but worry civil libertarians — Internet domain names.
In one case, the government took over Web sites that it said peddled bongs, roach clips, rolling papers and other paraphernalia used in the consumption of illegal drugs.
Prosecutors also acquired, in a plea agreement, a site called isonews.com whose owner was charged with selling special chips that let pirated titles run on videogame consoles.
In the past, Web sites simply vanished after the computer servers that hosted them landed in police property rooms. But in the recent cases, the sites remained alive, greeting visitors with stern warnings from government agencies.
The trend is alarming online civil liberties groups and legal scholars, who say the government's new tactic risks depriving people of valuable property — their Internet storefronts and thus their livelihoods — as electronic commerce becomes more common.
"If you want to take down a Web site but simply confiscate the servers, operators can always buy other servers," said Michael Overly, an attorney specializing in computer law at Foley & Lardner. "But if they take the domain name away, then they've put the person out of business."
Critics of the Justice Department's recent moves also say they fear the government could use the new method to spy on Web surfers who visit confiscated sites.
"The government is suddenly in a position of being able to monitor the Web-surfing activities of unwitting individuals who believe they are going to a Web site ... but possibly implicating themselves into some law enforcement investigation," said David Sobel, general counsel of the Electronic Privacy Information Center.
Visitors to pipesforyou.com, aheadcase.com and others are now greeted with a message informing them that a Pennsylvania federal court has "restrained" the sites at the request of the Drug Enforcement Administration.
In announcing the indictment last week of 55 people for allegedly selling drug paraphernalia on the Internet, Attorney General John Ashcroft said several sites had been redirected to DEA servers and that prosecutors had asked the court to redirect another "15 to 20 sites within the next 30 days."
The Justice Department did not return repeated phone calls seeking comment on what it plans to do with the sites and their visitor logs.
A DEA spokeswoman, Tara DeGarmo, noted that the domain names in the head shop case were "retained" but not seized pending the outcome of the criminal cases. She referred questions to federal prosecutors, who did not return calls.
That leaves privacy activists guessing.
"You can spin this out to future situations where there are a lot of classes of individuals the government might like to have a list of," such as visitors to terrorism- or biological weapons-related sites, Sobel said.
On the Internet, Web surfers are identified with a unique number, or Internet Protocol address. Devices on the Internet need such an address to send and receive Web, e-mail and other traffic.
Domain names are the Web's equivalent of the front door of a bricks-and-mortar business. But while businesses can physically relocate in the material world, in cyberspace they depend on their domain name. The physical location of the Web site is immaterial.
Among issues that remain unresolved in the courts is whether a domain name constitutes property, or a contract the owner has with the domain name registrar — the company that provided the name. If the former, a domain name could indeed be seized like a car, house or computer.
In the past, domain name registrars have sued to ensure that their offerings are not considered property. Otherwise, Overly said, "they would find themselves at the heart of no end of litigation."
The registrars involved in the head shop investigation either declined to comment or did not return telephone calls.
Domain transfers have in the past occurred as a result of criminal or civil cases, but Overly said the courts would ultimately decide the issue.
"The government has done many things over the years," he said, "that ultimately turn out not to be legal."