Tracking individuals is a major issue today. Several methods exist, but they are limited you to user interaction. A new way of tracking is based on Wi-Fi which does not need any user cooperation. However this method involves new privacy threats. This paper verify if the existing solutions to protect the privacy are secure enough. The tracking system is based on Wi-Fi sensors installed in different locations to monitor and record packets sent by Wi-Fi-enabled devices. The identification process is possible thanks to the MAC address contained in each packet. However this unique identifier is bound to the user and has to be securely stored. Tracking individuals has plenty of applications. Studying the habit of customers in shop center is a service offered by several new specialized companies. We analyze which kind of protection are used, where and how data are stored. One commonly used protection is the one-way hash function. Studying the MAC1 addresses' distribution leads us to develop an attack. Finally, a test platform is built to validate or not the solutions or think to new ones.