ABSTRACT The last decade witnessed significant research of user behavior and social networks within online hacker forums and illicit markets. Researchers have used the quantifiable nature of forum posting behaviors to assess network ties between actors and identify key participants based on their connections. These studies are based on the publicly identifiable associations between actors in public posts. Participants within forums can also connect with users through private messaging systems linking users directly through a sort of e-mail-based exchange. Few have considered how the public and private message networks of actors differ and what can be gleaned from their analysis. This study employed a quantitative analysis of a highly popular web forum used by hackers involved in both legal and criminal hacks. First, the networks were built of the relationships between 1,313 users across 12,531 threads and 19,862 public posts, and between those users’ 1,738 private messages. Then the centrality on hidden networks was estimated from the centrality on the visible networks. The implications of this study for policy and our understanding of online network structures are discussed.