A monitoring system that receives messages that are exchanged with the application server. Relationships between users are posited in response to the times at which the messages are received. A relationship between two users may be posited in response to receiving, at approximately the same time, two messages from the application server that are destined, respectively, for the two users. The near-simultaneous receipt of the two messages indicates that the two messages were sent from the server at approximately the same time, which, in turn, indicates that the two messages may correlate with one another. Further indication of a correlation between the messages, which may increase the level of confidence with which the relationship between the two users is posited, may be found by examining the respective sizes of the messages, which indicate the message types.