WiMAX is a telecommunication technology. It is based on IEEE802.16 family and provides the network service with large coverage, high data rate and mobility. Since IEEE802.16 series are connection-based wireless technologies, WiMAX is exposed to a special kind of DoS attacks which can target a specific victim connection without influencing the others. This paper will introduce this scrambling attack in WiMAX networks in detail and will provide a prevention approach.