SybilBelief, a semi-supervised learning framework, to detect Sybil nodes. SybilBelief it takes a of the nodes in the social network of the system and optionally, a small set of known Sybils as input. Then, SybilBelief propagates the label information from the known benign and/or Sybil nodes to the remaining nodes in the system. In SybilBelief, the authors process both synthetic and real-world social network topologies. SybilBelief is able to accurately identify Sybil nodes with low false positive rates and low false negative rates. SybilBelief is resilient to noise in their prior knowledge about known benign and Sybil nodes.