1. A method, comprising: reducing, by a system comprising a processor, a sampling size of a total population of on-line social network users based on a comparison of seed information to a population of the on-line social network users to obtain a reduced sampling of the on-line social network users; generating a social network graph based on the reduced sampling of the on-line social network users; comparing, by the system, the reduced sampling of the on-line social network users to the social network graph; and identifying, by the system, an outlier in the reduced sampling of the on-line social network users based on relationships between the on-line social network users, and based on collateral information combined with an intra-graph property of the social network graph, wherein the outlier does not conform to the social network graph.