A system comprising: one or more first user terminals each for a respective user, each of the first user terminals comprising a first interface to a service run over a communication network; an authorization mechanism arranged to conditionally verify the users of the first user terminals as being licensed to use the communication service based on a first indication received via the first interface; and one or more second user terminals each for a respective user, each of the second user terminals comprising a second, alternative interface to the communication service; wherein the second interface is not operable to provide the first indication to the authorization mechanism; and wherein the authorization mechanism is configured to conditionally verify the users of the second user terminals as being licensed to use the communication service based on a second indication received via the second interface.