Researchers from the U.K.'s University of Cambridge recently published a paper (PDF) detailing a project in which they developed a software tool to correlate and map Facebook profiles they found via public search engines, such as Google, to build detailed maps of relationships among Facebook members.
"We focused on inferring information about a whole social graph...lists of every person and the connections between them," such as group memberships they had in common or geographic ties, says Joseph Bonneau, one of the project's researchers.
Bonneau says marketers typically look online for the "best-connected" people who can influence others, so this type of information could be used to target them. And phishers or identity thieves could capitalize on this data, as well, according to the Cambridge research.
"You could do targeted phishing attacks if you knew people's [Facebook] friends and claim to be their friend," Bonneau says.
The researchers demonstrated how this "public search vulnerability" targets the entire Facebook network, not individual members, he says. "On the question of whether someone is a very important [or well-connected] person is difficult to tell with their specific profile, even if you have access to it," Bonneau says. "Facebook makes it difficult to crawl [this information], but it's easy to do in public search listings."
But Chris Kelly, chief privacy officer at Facebook, said public search listings are for members of the social network (but not minors) who want to have "limited elements" of their profile to be searchable online. They are able to configure their own public search listing.
"Changes as to the presence or content of a public search listing may be made easily by any user on the privacy settings page," Kelly said.
Facebook first introduced the public search listings feature last year.
Bonneau said Facebook members usually don't realize such a potential privacy hole even exists, he says. "They think it's just their friends who can see their data," Bonneau says, but they don't realize their privacy could be at risk via this larger group view of Facebook members.
The level of detailed information that could be gleaned is more about the member's relationships among other members, including geographic location and affiliations, he says.
Facebook automatically opts-in members to this public listing feature, which non-Facebook members can view, he says; many users don't realize they can opt out. For Facebook, it helps recruit more members to sign up for the social networking site, Bonneau says.
"Knowing who a person's friends are is valuable information to marketers, employers, credit rating agencies, insurers, spammers, phishers, police, and intelligence agencies, but protecting the social graph is more difficult than protecting personal data," the researchers wrote in their paper. "Personal data privacy can be managed individually by users, while information about a user's place in the social graph can be revealed by any of the user's friends."
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