8 friends are enough

New article by Ross Anderson’s group. It’s beautiful in its simplicity. “Eight Friends are Enough: Social Graph Approximation via Public Listings shows how easy it is for an outsider to work out the structure of friendships on Facebook. (For more, see our blog on Facebook’s technical privacy and its democracy theatre.) ”

In short: Having

  • G: undirected graph (e.g., Facebook social net)
  • Gk: publicly available portion of G (one in which k outgoing friendship edges have been randomly chosen from G),

they show that the results of applying a certain function f (e.g., centrality, shortest paths, community structure) on Gk are simlar to those of  applying f on the entire G! That is, by using the public view (Gk), one is able to infer node centralities, shortest paths, and community structures of the whole G! Scary result for privacy-conscius people! But good news for researchers who need to handle big networks ;-) On the scary side, from a partial (public) view of a social network, one is able to guess

  • which nodes are central – e.g., 1) marketing companies are able to  identify influential individuals and virally spread products through them; or 2) during protests that are self-orginized via text messages, repressive governments are able to identify influential individuals and intercept  their text traffic.
  • communities – the authors “were ableto divide the [partial] graph into communities nearly as well as using complete graph knowledge.” (Sect 3.5)

2 Responses to “8 friends are enough”

  1. Josh says:

    awesome. Thanks for pointing out this paper. I messed up one of my crawlers and only grabbed a known subset of friends from social network users instead of the complete list. I figured there would be something useful I could do with that data, but hadn’t sat down to go through it yet.

  2. TBW says:

    Algorithmically this is great. Most global algorithms on massive networks are impractical. This means that local calculations would serve as a pretty good proxy for many global properties and thus speed up many computations