Methods and systems for obtaining reconstructing activities of target users in social networks, such as for decoding and displaying social network sessions held by a target user, or identifying other users who are associated with the target user. This analysis is typically carried out based on passive monitoring of network traffic. A social network decoding system constructs and maintains a replica database, which mimics a portion of the user profile database maintained by the social network servers. The social network decoding system monitors network traffic between users and social network servers. Based on the monitored traffic, the system gradually constructs a replica database that attempts to replicate a portion of the social network user profile database, relating to one or more predefined target users. Using the replica database, the system is able to correlate loosely-coupled information objects, events and interactions between the target users and social network pages.