A system and method for correlating a user's use of a first network service with a user's use of a second network service. For each user with which the first network service communicates, the network service transmits a unique ID to the user such that the unique ID is visible to the user. When the user communicates with the second network service, the user provides the second network service with the unique ID. The first and second networks each may store some indication of their respective associations with the user. The user's use of the second network service is correlated with the user's use of the second network service based on the unique ID and any information stored by the networks in association with the unique ID.