Kathryn Hanson, a former telecommunications engineer who lives in Oakland, Calif., was looking at BBC News online last week when she came across an item about a British politician who had resigned over a reported affair with a "rent boy."
It was the first time Ms. Hanson had seen the term, so, in search of a definition, she typed it into Google. As Ms. Hanson scrolled through the results, she saw that several of the sites were available only to people over 18. She suddenly had a frightening thought. Would Google have to inform the government that she was looking for a rent boy - a young male prostitute?
Ms. Hanson, 45, immediately told her boyfriend what she had done. "I told him I'd Googled 'rent boy,' just in case I got whisked off to some Navy prison in the dead of night," she said.
Ms. Hanson's reaction arose from last week's reports that as part of its effort to uphold an online pornography law, the Justice Department had asked a federal judge to compel Google to turn over records on millions of its users' search queries. Google is resisting the request, but three of its competitors - Yahoo, MSN and America Online - have turned over similar information.
The government and the cooperating companies say the search queries cannot be traced to their source, and therefore no personal information about users is being given up. But the government's move is one of several recent episodes that have caused some people to think twice about the information they type into a search engine, or the opinions they express in an e-mail message.
The government has been more aggressive recently in its efforts to obtain data on Internet activity, invoking the fight against terrorism and the prosecution of online crime. A surveillance program in which the National Security Agency intercepted certain international phone calls and e-mail in the United States without court-approved warrants prompted an outcry among civil libertarians. And under the antiterrorism USA Patriot Act, the Justice Department has demanded records on library patrons' Internet use.
Those actions have put some Internet users on edge, as they confront the complications and contradictions of online life.
Jim Kowats, 34, a television producer who lives in Washington, has been growing increasingly concerned about the government's data collection efforts. "I'm not a conspiracy theorist, I just feel like it's one step away from ... what's the next step?" Mr. Kowats said. "The government's going to start looking into all this other stuff."
Until last year, Mr. Kowats worked at the Discovery Channel, and a few years ago, in the course of putting together a documentary on circumcision, he and his colleagues were doing much of the research online. "When you're researching something like that and you look up the word 'circumcision,' you're going to end up with all kinds of pictures of naked children," he said. "And that can be misconstrued."
"There're so many things you can accidentally fall into when you're surfing on the Internet," he said. "I mean, you can type in almost anything and you're going to end up with something you didn't expect."
Privacy is an elusive concept, and when it comes to what is considered acceptable, people tend to draw the line at different points on the privacy spectrum.
Ming-Wai Farrell, 25, who works for a legal industry trade association in Washington, is one of those who draw the line somewhere in the middle. They are willing to part with personal information as long as they get something in return - the convenience of online banking, for example, or useful information from a search engine - and as long as they know what is to be done with the information.
Yet these same people are sometimes appalled when they learn of wholesale data gathering. Ms. Farrell said she would not be able to live without online banking, electronic bill paying or Google, but she would consider revising her Web activity if she had to question every search term, online donation or purchase.
"It's scary to think that it may just be a matter of time before Googling will invite an F.B.I. agent to tap your phone or interrogate you," Ms. Farrell said.
Mike Winkleman, 27, a law student who lives in Miami and, like Ms. Farrell, belongs to the generation of people who came of age with the Internet, said he would like to think that the erosion of his privacy was for "a good cause, like national security or preventing child porn," he said. "But I can't help but feel that for each inch I give, a mile will be taken."
But Josh Cohen, a financial adviser in Chicago, identifies more closely with a subset of Internet users who see the loss of at least some privacy as the price they pay for being on the Web. Mr. Cohen, 34, said he was willing to accept that tradeoff in the pursuit of national security.
"We as U.S. citizens have got to start making concessions," he said. "In order for the government to catch people that prey on children, or fight the war on terror, they are going to need the help of the search engines."
Mr. Cohen said he doubted there would be much compromising of his individual privacy because the amount of data collected by the government was so voluminous. "My rationale tells me that with close to 300 million people in the U.S., and about 45 to 50 percent of households having Internet access, that I don't need to be too concerned with my search engine behavior," he said.
Susan P. Crawford, a professor at the Cardozo School of Law in New York, agreed that the sheer volume of information obtained by the government was likely to dilute privacy threats.
"More experienced Internet users would understand that in the mountain of search-related data available in response to a subpoena, it is very unlikely that anything referring to them personally would be revealed," Professor Crawford said.
She likened one's online activity to walking down the street. "We walk down the street all the time and we can be seen there," she said. "We also move around online, and can be 'seen' to some extent there as well. But we continue to go for walks."
Nevertheless, last week's court motion is giving some people pause. Sheryl Decker, 47, an information technology manager in Seattle, said she was now thinking twice about what she said in her personal e-mail correspondence. "I have been known to send very unflattering things about our government and our president," Ms. Decker said. "I still do, but I am careful about using certain phrases that I once wouldn't have given a second thought."
Ms. Decker's caution is being echoed by others. Genny Ballard, 36, a professor of Spanish at Centre College in Danville, Ky., said she had grown more conscious about what she typed into the Google search box. "Each time I put something in, I think about how it could be reconstructed to mean that I have more than an academic curiosity," Ms. Ballard said.
To be sure, Google is citing a number of reasons for resisting the government's subpoena, including concern about trade secrets and the burden of compliance. While it does not directly assert that surrendering the data would expose personal information, it has told the government that "one can envision scenarios where queries alone could reveal identifying information about a specific Google user, which is another outcome that Google cannot accept."
Ms. Hanson, who did the "rent boy" search, said that although she was aware that personal information was not being required in the Google case, she remained uneasy.
She pointed to a continuing interest she has in the Palestinian elections. "If I followed my curiosity and did some Web research, going to Web sites of the parties involved, I would honestly wonder whether someone in my government would someday see my name on a list of people who went to 'terrorist' Web sites," she said.
Mr. Kowats, the television producer, shares that fear. "Where does it stop?" he said. "What about file sharing? Scalping tickets? Or traveling to Cuba? What if you look up abortion? Who says you can't look up those things? What are the limits? It's the little chipping away. It's a slippery slope."