Abstract: Locationbased social network (LBSN) services enable users to discover nearby people. Original LBSN services provide the exact distances for nearby users. Existing studies have shown that it is easy to localize target users by using trilateration methodology. To defend against the trilateration attack, current LBSN services adopt the concentric bandbased approach when reporting distances. In this paper, by using number theory, we analytically show that by strategically placing multiple virtual probes as fake GPS, one can accurately pinpoint user locations with either accurate or coarse bandbased distances. As a proof of this concept, WeChat is examplified to validate that our attack methodology is effective in a realworld deployment. Our study is expected to draw more public attention to this serious privacy issue and hopefully motivate better privacypreserving LBSN designs.

Key words: locationbased social network, localization attack, WeChat