A Wireless Sensor Network (WSN) link layer security protocol called WSNSec is proposed in this paper. The effective usage of limited sensor node resources is of high importance in WSN security protocol design and implementation. In addition, research on increased security for the WSNs employed in especially military and health areas recently receives a remarkable attention as primarily focused on in this presented work. The WSNSec smoothly combines the advantageous aspects of the Scalable Encryption Algorithm (SEA) with the Counter Mode (CTR) and Cipher Block Chaining-Message Authentication Code (CBC-MAC) approaches. It provides not only high data confidentiality but also message authentication and integrity functions. The WSNSec security level can be boosted dynamically if required. It has been shown that using the proposed WSNSec with the 192-bit data block/key size has a trivial increase on the memory usage and energy consumption while providing an extremely high level of security compared to the traditional TinySEC. In addition, modeling and simulation of a WSN employing the proposed WSNSec have been realized using the OPNET Modeler software. The simulation results reveal that the ratios of the delays resulted from the particular use of both WSNSec and TinySEC to the total end to end delays converge at 13% for increasing the network load. Therefore the WSNSec provides a better delay performance in highly scalable applications. (C) 2011 Elsevier B.V. All rights reserved.