IEEE 802.11-based Wireless LANs (WLANs) are deployed in public places, universities, offices and shops. The main reason for the popularity is convenience of internetworking without wires. The increase in WLANs also resulted in increase of security threats. One of these threats is spoofing MAC address. Some WLANs use MAC filtering to allow stations with registered MAC addresses to use the network. The attacker has many tools like AirJack, WireShark to capture the packets in WLAN and find authorized MAC address. The attacker masquerades as an authorized station and can launch denial of service attack. This paper presents a power hopping technique which can be used by Access Points (AP) to discern the authorized packets from the masquerading packets and thus deny the attacker from using the system.