  Detecting and suspending fake accounts (Sybils) in online social networking
(OSN) services protects both OSN operators and OSN users from illegal
exploitation. Existing social-graph-based defense schemes effectively bound the
accepted Sybils to the total number of social connections between Sybils and
non-Sybil users. However, Sybils may still evade the defenses by soliciting
many social connections to real users. We propose SybilFence, a system that
improves over social-graph-based Sybil defenses to further thwart Sybils.
SybilFence is based on the observation that even well-maintained fake accounts
inevitably receive a significant number of user negative feedback, such as the
rejections to their friend requests. Our key idea is to discount the social
edges on users that have received negative feedback, thereby limiting the
impact of Sybils' social edges. The preliminary simulation results show that
our proposal is more resilient to attacks where fake accounts continuously
solicit social connections over time.
