A method is provided of anonymizing an interaction between a user entity and a service provider node wishing to provide a service to the user entity in dependence upon characteristics of the user entity determined or revealed as a result of the interaction, the method comprising: assigning the user entity to at least one set, each set comprising as members a plurality of user entities sharing a characteristic associated with that set; ensuring that the intersection of the at least one set comprises at least a predetermined minimum number of user entities; and providing to the service provider node information relating to the or each characteristic associated with the at least one set, the information being for use at the service provider node in providing a service to the user entity that is appropriate in view of the characteristics of the user entity but insufficient to identify the user entity.