Significant progress has been made to achieve video streaming over wireless ad hoc networks. However, there is not much work on providing security. Is existing security solution good enough for securing video streaming over ad hoc networks? In this paper, we discover a cross-layer dropping attack against video streaming. We first identify a general IP layer dropping attack and then reveal its destructive impact by leveraging the application layer information (e.g., video streaming). Through simulations, we quantify the impact of this attack as a function of several performance parameters such as delivery ratio, hop number and the number of attackers. The surprising result with this attack is that with a 94% delivery ratio, the receiver still cannot watch the video! We also propose several possible solutions to address the dropping attacks. Due to the unique characteristics of this attack, as long as malicious nodes exist, the network will suffer from this dropping attack.