A system and method are directed towards mapping a first user ID, such as an alias game ID, which may be used by multiple users, to a second user ID, such as a portal messenger ID. A user registers with an intermediary service, such as a game data aggregation service, and provides both the first user ID and the second user ID. The aggregation service detects when the first user ID is being used by one or more users in a first service, such as an online game service. The aggregation service also detects when a client probe reports to a second service, such as a portal messenger service, that the second user ID is participating in the same service. The aggregation service determines whether one instance of the first user ID from the first service corresponds to the second user ID from the second service.