It can help you find new friends, new businesses, but as many Facebook users are just finding out. It can help other people find things about you that you thought were private
"It looks like nothing's visible to an outsider," Lauren Levine said.
Levine cares a lot about her privacy.
"I don't even want to be on TV talking about this," she said. "But I think it's something that's really important. People don't know that this is happening."
We viewed Levine's Facebook profile from a stranger's account. Her privacy settings make nothing visible to anyone but her friends, until we clicked the little search box at the top of the page.
"And all kinds of menu options come up," she said. "Photos of me, friends of mine, photos by me."
That little menu is part of Graph Search. It rolled out over the summer. And a recent policy change says you can't opt out of it.
"Photos that I've commented on, photos that I've liked, photos that my friends have commented on," Levine said. "All kinds of things I had no idea was there."
Though everything Levine posts on Facebook is private, sometimes she's tagged or comments on a friend's picture that's shared publicly. And now, any stranger can look at all of those tags and comments right from her profile.
"It's just page after page after page after page," Levine said. "And it's really alarming."
After Levine brought the story to our attention, we rounded up a few volunteers who agreed to Graph Search themselves.
"Oh my gosh," said Dena Shapiro. "Oh, wow."
Shapiro is a teacher.
"I would've never wanted some of these to be up," she said.
Shapiro is worried about keeping her personal life personal.
"I want to be able to take a picture with a friend with a glass of wine, and I don't think my students and my students' parents need to see that," she said.
Our next volunteer, Craig Joyner, had a similar reaction. His friend tagged him in a post about his mother's 100th birthday.
"And it actually has my telephone number in that article," he said.
Their whole conversation in the comments was public.
"I feel like I need to become a former Facebook user, candidly," Joyner said.
If you're a private person, Facebook's becoming a difficult landscape.
The Electronic Frontier Foundation points out sharing is what Facebook's all about.
"But it's also incumbent on Facebook to help sure people understand and make sure there are no surprises and what information about them is available to others," Opsahl said." When asked if Facebook's doing an adequate job with that, he said, "I mean, your study seems to show that this is not working."
"There's a photo of me with JFK junior years ago," Harold Mann said.
For Mann, our last volunteer, it's the stuff he forgot was on Facebook.
"We easily start to forget how permanent these things are," he said. "We just make a quick aside and it's preserved for so long, I think that's the scary part."
Even scarier for kids; one reason Facebook does keep children from appearing in searches.
And Facebook says it's working to make sure adults can better understand its daunting array of privacy settings.
But with Graph Search it's not just your privacy settings that matter, it's your friends' privacy settings that determine which of their posts show up when someone searches for you.
Facebook hasn't responded to calls for an opt-out from Graph Search. And they declined our request for an interview.
The Electronic Frontier Foundation says your best defense is to be a good friend and ask your friends to do the same.
"Be cool, and don't spread around information that other people wouldn't' want spread around," Opsahl said.