Abstract: A fraud detection system is used with a communications network, the network including a billing system having a database of customer account information and of account-associated call logging information including called numbers. Each customer account includes customer name and address information and a settable indicator which when set indicates that the account is a debt account having a predetermined debt status. The fraud detection system is responsive to a debt account accessing, in use, the database for selecting a customer account, for obtaining a group of called numbers associated with the debt account and a group of called numbers associated with the selected customer account are compared. The respectively obtained groups and, if the degree of similarity of the calling characteristics of the two customer accounts meets a predetermined criterion, an indication that the selected customer account is a probable fraudulent-application account is provided.