The present invention relates to a method and network device for monitoring a party in a communication network, wherein a link information linking at least two types of identifier data for identifying parties to be monitored is stored, and a correspondence between the stored link information of the monitor party and identifier data supplied from the communication network for the monitored party is checked. A new link information linking supplied non-matching identifier data to a stored other type of the at least two types of identifier data linked by the stored link information is added to the stored link information, to thereby provide an automatic Subscriber Identity Module (SIM) infecting feature. Thereby, no connections are missed as each new set of identifier data generates a new entry in the database.