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How Friends of Your Friends Give Away Your Private Info Online

by Katie Moritz
May 18, 2018 | Our Future

Where do you stand when it comes to sharing your personal information online? Facebook CEO Mark Zuckerberg's April Congressional testimony could have been a sobering reminder that our private information is less and less private every day. Yet the public reaction was more like a collective sigh and eyeroll—and an avalanche of memes about Mark Zuckerberg's detached delivery and seating arrangement.

But maybe you're the type who's actually very worried—in 2016, about half of people in the U.S. said they were “very concerned” or “somewhat concerned” about government surveillance of their data, according to the Pew Research Center. Eighty-six percent of internet users have taken steps to mask their identities when they browse to protect their personal information.

Researchers who study the ways our data is accessed by people we don't want to have it are often finding new loopholes in the system—this scientist found that your location can be tracked by anyone for about $1,000. And another research team, Stanford University's Johan Ugander, assistant professor of management science and engineering, and Kristen Altenburger, a PhD student in his lab, recently discovered that the very most difficult information to swipe from us might be getting inadvertently leaked—not by the people closest to us, but by the friends of our friends.

Like goes with like—most of the time

A lot can be learned about us from our behaviors online—mark yourself as "married" on Facebook and you might start getting ads for baby stuff. Shop for a toilet seat, and you might get ads for more toilet seats.

Group of male Friends Meeting In Café Restaurant. Private Info pbs rewire
"I can't wait to get targeted ads about this later."

Looking at our friends can reveal some of the same stuff. Past research on social media friendships has shown that we're overwhelmingly friends with people of the same age, race and political beliefs as our own, according to a Stanford University news release. (Researchers call our love of sameness "homophily.") That means even when we don't share that information with companies, it can be easily figured out just by looking at who you associate with online.

But some of your traits can't be easily figured out by looking at your online friends. Surprisingly, one of the toughest to suss out is gender. If you have a lot of male friends, you're just as likely to be female as you are male, Altenburger said in the release.

The 'secrets' our network can reveal

That can change when you zoom out to your larger social network. By looking at the friends of your friends, people who want to can figure out hidden information that's more difficult to ascertain, especially your gender.

By looking at tons of social network data with the gender information removed, Ugander and Altenburger discovered a common social structure that's different from homophily—something they're calling "monophily," Greek for "love of one." Monophily in a social network occurs when someone has extreme preference for a trait, but not necessarily a trait of their own.

“For example, on average it might be the case that men don’t have a clear preference for male or female friends, but that average may be obscuring the fact that some men have strong preferences for male friends while others have strong preferences for female friends,” Ugander said in the release.

By looking at patterns within your friend's friend group, entities looking to gain access to your information can make educated guesses about you. Surprisingly, you might have more in common with the friends of your friends than with your friends.

Happy positive young woman holding her smartphone and showing in to her colleagues while interacting with them. Private Info pbs rewire
Keep your friends close, and your friends of friends closer.

“It’s a fill-in-the-blanks problem,” Ugander said. “And while we find that your friends don’t tend to predict your gender, the people those friends choose to associate with, your friends of friends, tend to be more similar to you than even your friends are.”

In 2014, the Pew Research Center found that 91% of people in the U.S. “agree” or “strongly agree” that people have lost control over how personal information is collected and used. To the researchers, their discovery means the body of information we can truly hide online is still shrinking. And it means "that not only should data-privacy preserving approaches continue to consider the similarity" between friends, Altenburger said to Rewire, but that additional attention should be put toward what can be learned from our wider networks, too.

She said it'll take more research to figure out how exactly social media users can guard against potential data harvesting through friends-of-friends. For now, check out these ways to lock down your information on Facebook as best you can.

Katie Moritz
Katie Moritz was Rewire's senior editor from 2016-2020. She is a Pisces who enjoys thrift stores and pho. Follow her on Twitter @katecmoritz.
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