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A pulled pork taco hovered about four inches from my mouth when my phone impolitely interrupted me. “Hey, I see you’re having people over. O.K. if I stop by?” read a text message from someone whom I had not invited to my dinner party.

How did the person know I was even having a party? I needed only to glance at my guests, who were sharing messages and photos of the dinner to their online social networks.

Call it the latest episode of “Nothing’s Private Anymore.”

While you’re going about your daily life, stopping to get coffee with a crush, meeting friends for drinks or going to a Madonna concert, people are watching you on Twitter, Facebook, Foursquare, Path and an interminable list of other social networks.

“But wait,” you’re saying to yourself, “I didn’t ask to be on this show.” [Laughter from the audience.] Too late — you have no choice.

“But … but … I didn’t update any of these services to announce what I’m doing. I’m not even on Facebook.” [More laughter.] You don’t have to be, since other people can announce your location, and share pictures and videos of you, conveniently tagged with your name for anyone to find quickly.

Social stalking doesn’t just happen to people like me, an inveterate social networker who covers this subject for work; it happens to normal people, too. While it can be merely a nuisance when others put you on public view, it can have serious unintended consequences when people discover things you had intended to keep private.

Your former spouse is watching. Your boss? Yup, she’s watching, too. Your mother, father and probably Uncle Pete.

This happened at the dinner party I had last week.

What else besides tacos was on the menu? Well, that isn’t hard to determine either.

I certainly didn’t tweet or share information like that on Facebook, but many of the 15 people in attendance did.

I know that because a few days later, on a work-related call, someone else — who has never stepped foot in my house — told me how much he “just loved” the lamps hanging above my kitchen table.

Over the course of the three-hour dinner, my friends posted seven photos on Path, sent six Twitter messages (five with photos), six photos on Instagram and two people checked in on Foursquare.

When I added up the collective follower counts of the people in the room, my little dinner party was potentially viewed by more people than watch “The Late Show” on CBS: over three million. (Granted, the guests included social media heavyweights like Om Malik, founder of the popular tech blog GigaOM, and Veronica Belmont, an online video host with 1.6 million Twitter followers.)

“I don’t think it’s the norm for most people yet; it is though for the microcosms that are Silicon Valley or South by Southwest,” said Dennis Crowley, the chief executive of Foursquare. “But, at the same time, I think those things predict the future and the way the tech elite act now is the way everyone will experience the world a few years from now.”

Before that happens, customers might force companies into letting them “cloak” themselves for a particular time period. “You can imagine a service that says ‘I don’t want my name to show up on any social services for the next three hours’ and then integrates with other social services,” Mr. Crowley said.

A feature that allowed users to opt out of being mentioned could actually benefit companies like Facebook and Twitter. It would entice people who are afraid of being in the cast of “Nothing’s Private Anymore” to sign up, knowing that they can hide at any given time.

Mr. Malik said he had simply resigned himself to the reality that most of the things he does in public, no matter how banal, will end up on the Internet. “But an offline switch would be a welcome addition for it would give me an illusion of privateness (if not privacy),” he wrote in an e-mail.

But until that exists, if I don’t want people sharing pictures of me at a dinner party, I may have to resort to posting an old piece of technology called a sheet of paper with the message (in less than 140 characters): “Please don’t check in on Foursquare, Facebook, Twitter, Path, Myspace or any other service. #thanks!”