It is provided a method, comprising monitoring, for each of plural attempts of a web identity to register for an internet protocol multimedia service, if the respective attempt is received; generating, for each of the plural attempts if the respective attempt is received, a respective private user identification based on the web identity and a respective distinguishing identifier, wherein probability that two of the private user identifications have a same value is less than a predefined limit; providing the respective private user identification in response to the respective attempt.