Abstract: A method of, and a system for, detecting possible fraudulent use of a telecommunications network. Call event records, both call initiation and call completion records, are examined. A call record has a number of key fields, e.g. called number, calling number, calling card number, and for each field in turn the key is used to access a database containing an associated set of profiles. Each profile contains an algorithm defining a measurement process to be performed on the call data, e.g. determine the call duration. The respective process results are added to a respective set of stores associated with each profile, and an alarm response is generated when a threshold of a store is reached. An additional process for e.g. a call duration of e.g. called number card calling number key fields, convert the process results to penalty points which are added to a penalty points store associated with the calling card number key of the call event record under examination.