Browse any Facebook profile set up by a relatively active user and you're likely to hit on a cache of personal information that, until very recently, would've been impossible to get unless you hired a private detective to follow the person for six months.

Facebook, of course, is the red-hot online social network that recently opened its doors to the public, a move that helped it attract more than 26 million visitors in May, an almost 90 percent increase from a year earlier, when the Web site was open only to students.

Aside from the usual reams of biographical data on a user's page — birth date, hometown, schools, religion, relationship status, blog address, etc. — you'll be offered a list of the person's friends and acquaintances, broken into convenient categories: school, region, workplace and common interests. Likely as not, the profile also will list this individual's favorite bands, the cities he or she has traveled to, and a few notes about what he or she has done that day. In many cases, you'll have access to hundreds of photos, each one conveniently "tagged" with the names of all the people who appear in it.

And to think, until you spent that 20 minutes poring over this complete stranger's profile, you didn't know a thing about him. But now you do. A lot.

Stalker.

Yes, you're guilty: In the world of social networking, keeping tabs on people without announcing yourself is known affectionately as "profile stalking." But there's a key difference between old-fashioned, binoculars-and-bushes stalking and the online kind. One is for creeps and deviants. The other, explained University of California, Berkeley, anthropologist Danah Boyd, is for everyone.

"We all do it," she said, just like we all "ego surf" — or Google ourselves.

Profile-stalking is just the newest way to satisfy our "deeply ingrained desire to know," Boyd said. The more we're in the loop about people, the more control we have over our situation — or so we believe. We're most intrigued by people we're attracted to, whom we admire, who can help our careers. Some people we're just plain curious about. "What's the harm in following a little bit of their lives?" Boyd said.

Boyd admitted to her own recent adventure in profile stalking. After a bit of "ego-surfing," Boyd stumbled on a Trinidadian teenager who shared her oddly spelled first name.

Although Boyd had almost nothing in common with her namesake, she felt drawn to the girl's story and began fastidiously keeping track of her through her various online profiles. "It's a life so different than my own — I just find it fascinating," Boyd said, adding that the interest was purely passive — she had no interest in actually contacting the girl.

"Don't be so obsessive that you become visible in your stalking" is Boyd's rule of thumb.

A brief pause, in the interests of bridging the generation gap. (Meaning: The next two paragraphs are aimed at anyone older than, like, 22.) If you're having trouble understanding why anyone would want to spend time snooping on another person's online profile rather than, say, watching a Frank Capra film or working in the garden — here's a thought experiment:

Think of the one person from your past on whose life you would most dearly like to be brought up to speed, former lovers and estranged friends being the most obvious examples. Now imagine that you have a window into this person's life in the form of frequent newsletter updates, scores of recent photos and a list of active acquaintances. If you would have a difficult time keeping yourself from checking this person's profile, you're getting the picture.

These profile-stalking stories abound. San Francisco blogger Beth Prouty became intrigued by the profile of a raven-haired Oakland, Calif., woman who wrote about having intense and disturbing dreams as a result of her medication. Prouty identified with the woman because the same thing had happened to her two years before.

Although the 23-year-old Prouty felt that sharing her experience with the woman might help her, she decided it wouldn't be appropriate to contact her out of the blue. So instead, she began to check the woman's profile several times a week to keep up on her life.

"People like to watch. We've cultivated that through television and movies," said Prouty. "People are voluntarily putting up their real lives — it's like reality TV to the next level."

Eventually, Prouty wrote a somewhat lengthy missive to the woman (whom she preferred not to name for this article), mentioning the dream connection and telling the woman she seemed "lively and cool."

The woman replied with a modest thank-you. Prouty then sent a second e-mail, even longer than the first. This one received no reply.

"I don't know what to chalk it up to," said Prouty, citing her own "verbosity" or the other woman's laziness as possible causes for the shutdown.

What seems most likely, however, is that she violated Boyd's "stay invisible" rule. Stalkers can look, but if you touch, you risk freaking someone out.

Proctors at Oxford University showed their ignorance of the invisibility precept as well. Last week it emerged that school officials were digging around in students' Facebook profiles, looking for photos of kids engaged in "trashings," a post-exam ritual whereby students celebrate by splattering each other with eggs, flour and pet food. According to a report on Telegraph.co.uk, cleaning up the resulting mess costs about $41,000 annually. The proctors sent disciplinary letters to any students whose profile photos revealed egg on their faces.

A representative from Oxford's Student Union called the school's response to the widespread dog-food vandalism "disgraceful and underhanded."

Although it's true that Oxford officials were never invited to look at student profiles, the students had not set their profiles to private.