Abstract: Increased network security is provided by monitoring in real time one or more characteristics or attributes of telephone calls that are placed through the network and notifying the network customer (i.e., the party responsible for paying for the telephone calls), in real time, when the attributes are indicative of abnormal or fraudulent network usage. The network customer, once notified of the abnormal usage, is in a position to take steps to minimize unauthorized network usage. For example, the network customer can selectively block network usage, deny access to the network on a call-by-call basis, or trace the call to catch the unauthorized user while the call is still in progress.