The other day on the Internet, one man’s Facebook circle received a public service announcement of sorts: This goes out to any girl that ive ever been with. I got tested today for Herpes and i came out positive.

Privacy just isn’t what it used to be.

With Facebook at the forefront, social networking companies with business models hungry for personal data and a youthful generation raised on the Internet seem to be pulling the 21st century toward a more “transparent” culture, in the approving words of Mark Zuckerberg, the social networking giant’s 26-year-old founder. Facebook’s stated mission: “Giving people the power to share and make the world more open and connected.” In other words, letting more people know more about each other.

This comes as long-standing social mores and sensibilities are being shaken by the convergence of Silicon Valley technologies. Besides Facebook, which is based in Palo Alto, sites such as Twitter and YouTube are encouraging hundreds of millions of people to share information and images. Gadgets developed here, from the PC to the iPad, have made it simple for users to create, communicate and access that vast amount of digital data. And Google, Yahoo, Microsoft and others have made it easier to find all of that information.

“Facebook has indeed changed the nature of privacy on the Internet, in that it actually encourages people to make maximum disclosure of their personal information without regard for the possible consequences,” said Robert Ellis Smith, publisher of Privacy Journal, a publication that since 1974 has tracked the impact of technology and law on privacy. “Facebook involves lots of young persons who either are not old enough to give meaningful consent or have not had enough life experience to know the consequences.”

The defining acronym of our time may be TMI, the text-message shorthand for “too much information.” In the six years that Facebook has turned its “sharing” service into a global phenomenon approaching a half-billion users, a Nexis search of major newspapers found a 2,000 percent increase in the use of the term “oversharing.”

The hazards of TMI can range from embarrassment and job dismissals to fraud. PleaseRobMe.com, a website that uses Twitter’s search capability, was set up to highlight how people’s willingness to disclose their whereabouts makes their homes vulnerable to burglars.

Attitude vs. behavior

Facebook, Twitter and other companies, many consumer advocates and some lawmakers say, should do more to protect users who may not understand how widely their data is exposed.

Laws to strengthen personal rights on the Internet, some argue, must also anticipate the unintended consequences of advancing technologies. Improvements in facial recognition, for instance, could result in identifying the individuals in the vast numbers of photos and videos on the Web — whether they want to be or not. As it is, individuals have no control over whether their images are posted by others, or comments made about them.

But the companies driving the TMI trend argue that users post information voluntarily. And a close examination of Internet use, scholars say, reveals a disconnect between individuals’ expressed attitudes about privacy and their behavior.

“People report in studies that they care deeply about privacy,” said Ryan Calo, a fellow at Stanford Law School’s Center for Internet and Society. “But then people don’t seem to act in a way that protects their privacy.”

The conclusion many researchers and advocates draw is not that actions speak louder than words, but that the economic interests of many Internet companies are served by users’ ignorance.

“Right now, many companies are trying to get as much information as they can because it’s so valuable,” Calo said. Consumers would find reason for pause, he suggested, if they contemplated “these privacy policies that nobody reads.”

In fact, the term “privacy policy” was found to give people a false sense of security, according to a study led by Chris Hoofnagle, director of the UC Berkeley Boalt Hall School of Law’s Center for Law and Technology.

Privacy not a default

Facebook, the dominant force in online social networking, has been criticized for what one analyst called its “ready, fire, aim” approach to privacy policies. Initially tailored for university communities, Facebook has steadily broadened its default privacy settings in a way that exposes as much of a user’s posted information on the Web as possible unless users customize those controls.

Zuckerberg and his lieutenants argue that the site’s privacy controls strike a proper balance, noting that more than half of Facebook users have used the service’s settings either to restrict data or make it more open. The company also says it actively polices the service, banishing third-party application providers suspected of violating Facebook’s privacy policies.

Facebook’s collegiate roots have helped foster the popular view that young adults, having grown up with the Internet, are less worried about personal privacy than their elders. But that notion has been called into question by recent surveys led by Hoofnagle and by the Pew Center for the Internet and Society that found keen interest regardless of age.

Younger adults, the studies found, were actually more likely to actively “manage” their online data, rather than acquiesce to Facebook’s default settings.

On the other hand, older adults have been more likely to shun online social networks entirely, or generally be less active users and accrue fewer online “friends.”

Privacy, researchers say, is a shape-shifting concept that means different things to different people at different points in their lives. Life experience, Smith and Hoofnagle point out, often makes people more circumspect.

Strategic networking

Outside a Starbucks near Santa Clara University, Amina Beslagic and Sedina Jusic, both 22, said they took care to tighten their privacy settings to ensure their data is shared within their personal networks, each numbering more than 200 friends. But, they say, some of their friends and teenage siblings seem much more extroverted on Facebook.

“Younger kids, they don’t really care,” Beslagic said.

As Beslagic described it, an incident in the workplace prompted her to restrict her profile further. A colleague she’d never met in person said he had looked up her Facebook profile. Although it contained nothing she considered embarrassing, Beslagic said she was concerned that he might look up friends’ profiles and see photos of them “drinking and everything that goes with it.” Beslagic then decided to restrict the identity of her friends.

Inside San Jose’s Martin Luther King Jr. Library, 23-year-old Jessica Kalapin said she had 222 people in her Facebook network, and she finds it valuable to stay in touch with friends and family in Hawaii and Guam. Kalapin said she’s been careful about privacy settings since she signed up two years ago: “It’s only open to my friends.”

At another computer, 50-year-old Anthony Sims said he had about 30 friends in his network and was comfortable with the default settings. “It’s not like I have anything to hide,” he said. Sims said he believed that older users like himself are probably more careful about what they say online.

TMI ‘to the fifth degree’

TMI can result from ignorance or accidents. Many Facebook users may be familiar with seeing “status updates” from friends that were clearly intended for one person, not the entire group. And in researching this report, a Mercury News reporter who searched the term “abortion” uncovered a terse message on a woman’s profile indicating she was at a clinic and feeling “so sad.”

Efforts to reach the woman who had apparently posted the message were not successful. It was not clear that she meant this message for the more than 1,000 people in her Facebook network — as well as any Facebook user conducting such a search.

But she was not alone in exposing what many would consider intensely personal information. Another woman posted a message announcing she had just learned her sister was pregnant and that it was “abortion time.”

The context and veracity of messages observed in this manner is hard to determine. While some herpes comments appeared to be pranks played in mischief, others appeared sincere. One high school senior in Kentucky who shared his diagnosis with more than 500 people on his Facebook network was contacted by the Mercury News. He indicated that it was no joke, describing his condition as “herpes to the fifth degree.”

Such candor on the Internet, some public health advocates say, may provide a service by helping lift the stigma and silence that abets the spread of sexually transmitted diseases.

But some people, others point out, may live to regret the way a moment of indiscretion can come back to haunt them, in ways they may have never imagined. A case of herpes, Hoofnagle noted, can inspire a lawsuit — and a comment on Facebook could wind up as evidence in court.

Contact Scott Duke Harris at 408-920-2704.