Abstract: The invention relates to a mobile communication system including mobile stations, a mobile switching center, and a subscriber register containing subscriber data, which includes location information indicating the location of mobile stations. In order to detect the presence of a fraudulent mobile station the system includes a monitor for monitoring the processes which trigger location information changes in the subscriber register, and a detector for detecting and indicating the presence of a fraudulent mobile station if a location information change has been triggered by a process which should not trigger a change of location information in the subscriber register.

Abstract: The invention relates to a mobile communication system comprising: mobile stations (MS, MS′), a mobile switching center (MSC1), and a subscriber register (VLR1) containing subscriber data, which includes location information indicating the location of mobile stations. In order to detect the presence of a fraudulent mobile station the system comprises: monitoring means (1) for monitoring the processes which trigger location information changes in said subscriber register (VLR1), and detecting means (2) for detecting and indicating the presence of a fraudulent mobile station (MS′) if a location information change has been triggered by a process which should not trigger a change of location information in said subscriber register (VLR1).