The extended version makes the following additional contributions over the conference paper: (1) it provides a more detailed description of the attack; (2) it describes how the user uses WiGuard to protect sensitive information and gives the user a choice for the position and channel to optimize the system performance; (3) it provides new experimental results to evaluate the influence of the packet loss rate on the success rate and provides proof for the channel switch; (4) it adds a new experiment to evaluate the diversity of the attacker wireless transmitter; (5) it includes new results to compare the recognition results with and without channel interference. ‡ Jie Zhang and Meng Li are co-first authors.