Abstract: A system and method is provided for detecting fraudulent use of a unique identifier associated with an authorized mobile station in a wireless telecommunications network. A monitoring system passively collects data associated with the registration of one or more mobile stations utilizing the unique identifier. A fraud detection processor analyzes the collected data using a first pattern recognition device. The pattern recognition device determines the periodicity of successive registration messages associated with the unique identifier of the authorized mobile station and a suspected fraudulent event is identified when the time between successive registration messages is non-periodic. A second pattern recognition device may be utilized alone or in combination with the first pattern recognition device to identify suspected fraudulent activity when an apparent velocity of the mobile station utilizing the unique identifier between successive registration messages exceeds a predetermined maximum velocity.