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Deanonymization: Definitely Not Delovely

Earlier this evening I found myself perusing Facebook’s privacy policy. Facebook writes in reassuring tones that don’t reassure:

We only provide data to our advertising partners or customers after we have removed your name and any other personally identifying information from it, or have combined it with other people’s data in a way that it no longer personally identifies you….

Your trust is important to us, which is why we don’t share information we receive about you with others unless we have:

  • received your permission;
  • given you notice, such as by telling you about it in this policy;
  • or removed your name and any other personally identifying information from it.

Of course, for information others share about you, they control how it is shared…. When others share information about you, they can also choose to make it public.

Information that is always publicly available
The types of information listed below are always publicly available, and they are treated just like information you decided to make public:

  • Name:
    This helps your friends and family find you. If you are uncomfortable sharing your real name, you can always delete your account.
  • Profile Pictures and Cover Photos:
    These help your friends and family recognize you. If you are uncomfortable making any of these photos public, you can always delete them. Unless you delete them, when you add a new profile picture or cover photo, the previous photo will remain public in your profile picture or cover photo album.
  • Networks:
    This helps you see who you will be sharing information with before you choose “Friends and Networks” as a custom audience. If you are uncomfortable making your network public, you can leave the network .
  • Gender:
    This allows us to refer to you properly.

Did you notice how the information that Facebook promises not to sell is the information it tells you will be always publicly available anyway? Conversely, the information Facebook hasn’t made available to everyone is the information that it intends to sell. It’s all going to be available one way or another… but don’t worry, says Facebook, most of it won’t be “personally identifying information.” It’ll be de-personalized, we’re told, not connected to us.

Some worrisome “accomplishments” by computer scientists in recent years cast doubt on the assurances by Facebook and other social media giants. Our nation’s best minds have figured out how to “de-anonymize” your data … how to take anonymous internet posts from various sources and, by putting them together, figure out just who you are. A tip of the pen to Jennifer Golbeck, whose recent book draws my attention to this 2010 study, in which University of Maryland researchers were able to unmask the identity of three “pseudonymous” bloggers writing under fake names. When the authors interviewed these bloggers, they found out that each had good reason to conceal his or her identity. “Quirky Slut,” one of the three bloggers, wrote about her active and varied sex life and worried about whether her activities would cause problems in her social life if her identity was revealed. By paying close attention to occasional odd pieces of information mentioned in Quirky Slut’s blog, and by purchasing information on Americans gathered from various sources by the Alesco Data Group, the UMD team was able to pin down the likely identity of this blogger, even though she had never revealed any names, contact information, phone numbers or other unique information about herself. It was only the combination of various general pieces information that nailed down the identity of Quirky Slut. A short passage from their paper:

In the FAQ page of her blog she wrote “I live in the Albuquerque, NM area.” No more specific geographic detail could be found. The greater Albuquerque metropolitan area is comprised of 44 different zip codes, so by living in a big city and being consistently vague, Quirky Slut is actually doing a pretty good job of protecting her anonymity.

On September 19, 2007 Quirky Slut wrote “My birthday is over. So long teenage years.” She had a previous post on September 17 in which she made no mention of her birthday, so September 18 is most likely the day. She most likely turned 20 that year, making her birth year 1987. Later, on March 25, 2009 she confirmed the year when she described an upcoming vacation. “We can really enjoy Las Vegas since we’re both 21 now,” she wrote.

In her entry on August 19, 2009, Quirky Slut disclosed her marital status when she wrote “I’m not married, nor am I attached to anyone.” She revealed her dwelling size on April 19, 2007 when she described her living arrangements, “Well, I sort of live with my parents but I live in an apartment above the garage they used to rent to students.” This will actually turn out to be the crucial piece of access enabling information that will yield a high
probability of uniquely identifying Quirky Slut.

The following criteria were used to create an Alesco leads list:
• Zip Code: 44 selected for the entire Albuquerque area
• Age: 20-21
• Gender: Female
• Marital Status: Single
• Dwelling Size: Single Family Home
The returned list included just 72 names.

Of those 72 names, just one name had a birthday of September 18, 1987. Quirky Slut’s blog has since been taken offline.

Other academics have developed bulk methods for discovering the names of large numbers of people hiding behind anonymous social media accounts. Take this pair from the University of Texas at Austin, who reveal a method for obtaining the identities of anonymous Twitter users who also use the photo-sharing service Flickr. By looking for similarities in the patterns of connections to others made in the Flickr and Twitter networks, they’re able to identify anonymous Twitter users with a success rate of 88%.

You may not use your name. You may not share your contact information. But people who are willing to work hard enough may be able to find you nonetheless.

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