Wireless Sensor Networks (WSNs) facilitate efficient data gathering requirements occurring in indoor and outdoor environments. A great deal of WSNs operates by monitoring the area-of-interest (AOI) and transmitting the obtained data to a sink. The transmitted data can be utilized for object detection, object classification, instance localization, and high level semantic information extraction processes. In this regard, security of raw and relayed data is both crucial and susceptible to malicious attempts targeting the efficiency of the network. In this study, we focus on the effects of selective forwarding attacks taking place in the network layer and highlight possible impacts of successful attacks through experiment. Our analysis and evaluations are done on a selected sensor network information fusion architecture. According to the obtained results, selective forwarding attacks are hard to detect and have a significant effect on the efficiency of wireless sensor networks.