Various types of monitoring systems are used for tracking and/or collecting information on cellular phones or other wireless communication terminals. Some monitoring systems solicit a tracked terminal to reveal its International Mobile Subscriber Identifier (IMSI). Such systems are commonly referred to as “IMSI catchers.”
Examples of IMSI catching techniques are described, for example, by Strobel in “IMSI Catcher,” Jul. 13, 2007, by Asokan et al., in “Man-in-the-Middle Attacks in Tunneled Authentication protocols,” the 2003 Security Protocols Workshop, Cambridge, UK, Apr. 2-4, 2003, and by Meyer and Wetzel in “On the Impact of GSM Encryption and Man-in-the-Middle Attacks on the Security of Interoperating GSM/UMTS Networks,” proceedings of the 15th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Barcelona, Spain, Sep. 5-8, 2004, pages 2876-2883, which are all incorporated herein by reference.