Method of determining fraudulent use based on behavioral abnormality starts with processor receiving first location data and first proximity information from first mobile device. First proximity information includes identification of mobile devices within proximity sensitivity radius of first mobile device. Processor determines whether first location data and first proximity information are included in historical location data and historical proximity information, respectively, associated with first mobile device. When first location data and first proximity information is not included, processor determines whether subsequent location data and subsequent proximity information received from first mobile device over predetermined period of time is included. Processor signals to monitor fraudulent use of first mobile device when subsequent location data and subsequent proximity information received from first mobile device over predetermined period of time is not included in historical location data and historical proximity information, respectively, associated with first mobile device. Other embodiments are described.