He was a carefree Italian with a recent law degree from a Roman university. She was “a totally Virginia girl,” as she puts it, raised across the road from George Washington’s home. Their romance, sparked by a 2006 meeting in a supermarket in Rome, soon brought the Italian, Domenico Salerno, on frequent visits to Alexandria, Va., where he was welcomed like a favorite son by the parents and neighbors of his girlfriend, Caitlin Cooper.

But on April 29, when Mr. Salerno, 35, presented his passport at Washington Dulles International Airport, a Customs and Border Protection agent refused to let him into the United States. And after hours of questioning, agents would not let him travel back to Rome, either; over his protests in fractured English, he said, they insisted that he had expressed a fear of returning to Italy and had asked for asylum.

Ms. Cooper, 23, who had promised to show her boyfriend another side of her country on this visit — meaning Las Vegas and the Grand Canyon — eventually learned that he had been sent in shackles to a rural Virginia jail. And there he remained for more than 10 days, locked up without charges or legal recourse while Ms. Cooper, her parents and their well-connected neighbors tried everything to get him out.

Mr. Salerno’s case may be extreme, but it underscores the real but little-known dangers that many travelers from Europe and other first-world nations face when they arrive in the United States — problems that can startle Americans as much as their foreign visitors.

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Though citizens of those nations do not need visas to enter the United States for as long as 90 days, their admission is up to the discretion of border agents. There are more than 60 grounds for finding someone inadmissible, including a hunch that the person plans to work or immigrate, or evidence of an overstay, however brief, on an earlier visit.

While those turned away are generally sent home on the next flight, “there are occasional circumstances which require further detention to review their cases,” Ms. De Cima said. And because such “arriving aliens” are not considered to be in the United States at all, even if they are in custody, they have none of the legal rights that even illegal immigrants can claim.

In questioning Mr. Salerno, customs agents seemed to suspect that he intended to work here. Ms. Cooper, a copy editor for an educational publication, said she was in the airport lobby when an agent called to ask about Mr. Salerno’s income and why he visited so often...

Ms. Cooper said that at the airport, when she begged to know what was happening to Mr. Salerno, an agent told her, “You know, he should try spending a little more time in his own country.”

Twelve hours later, when Mr. Salerno was granted a five-minute phone call, he called Ms. Cooper and denied saying anything of the kind. Instead, he said, the asylum story seemed to be retaliation for his insisting on speaking to his embassy.

After being turned over to Immigration and Customs Enforcement, he was taken to the Pamunkey Regional Jail in Hanover, Va., where he ended up in a barracks with 75 other men, including asylum-seekers who told him they had been waiting a year.

Ten days after he landed in Washington, Mr. Salerno was still incarcerated, despite efforts by Senator John W. Warner, Republican of Virginia, and two former immigration prosecutors hired by the Coopers.

“He’s just really scared,” Ms. Cooper said in an interview last Thursday. “He asked me if Virginia has the death penalty.”

The Association of Corporate Travel Executives (ACTE) is warning its members to limit the amount of proprietary business information they carry on laptops and other electronic devices because of fears that government agents can seize that data at U.S. border crossings.

The group is worried that corporate data could be downloaded by agents, leading to potential security breaches and the exposure of information that is supposed to be private. Among the devices that could be searched by border agents are cell phones, handhelds, digital cameras and USB storage devices.

The warning follows a recent ruling from the Ninth Circuit Court of Appeals that basically upheld the right of U.S. Customs and Border Protection officials to search laptops and other electronic devices at U.S. borders without reasonable cause or suspicion.

The appeals court decision involved an individual who was arrested in 2005 on charges of child pornography after a warrantless search of his computer by customs officers at Los Angeles International Airport. A district court judge had previously ruled that the evidence presented by the prosecution should be suppressed because it was gained via an unreasonable search. That decision was later overturned.

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Many companies, especially in Europe, are having compliance officers look at the broader implications of such searches and have begun curtailing the kind of information their executives can carry on their laptops when traveling to the U.S, she said.

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"There may be some legitimate reasons for wanting to look at the data" on a traveler's electronic device, Gurley said. "But what are the parameters for such searches? Once they have the information, what do they do with it? What are the policies for retention and for data destruction? This shouldn't be such a hidden secret."