1. IntroductionDevelopments in microelectromechanical systems (MEMS) and wireless networks are opening a new domain in the history of networks. Sensors; often called "smartdust" are small, low-cost devices with limited coverage, low power, smaller memory size and low bandwidth, they will play a key role in collecting and disseminating data from fields where ordinary networks are unattainable for various environmental and strategic reasons. There have been significant contributions to overcome many weaknesses in sensor networks such as coverage issues, lack of power and better use of limited network bandwidth; work in the field of sensor network security is still at an early stage. This paper is an effort to introduce security issues in wireless sensor networks, highlight current research efforts, and determine future directions for solving unsolved problems. The remainder of this paper is organized as follows. Section 2 provides a brief overview of wireless sensor networks, their evolution, key research initiatives, and future applications. In section 3, security issues and challenges are discussed. Section 4 highlights related work in sensor networks. Section 5 concludes the paper by asking some questions and future directions.2. An Overview Sensor networks are emerging technologies currently used in seismic monitoring, wildlife studies, manufacturing, and performance monitoring. These sensor nodes are densely distributed in a predetermined geographic area to self-organize into ad hoc wireless networks to collect and aggregate data [8]. The ad hoc nature of sensor networks poses unique challenges in terms of security and reliability. Resource constrained sense...... middle of paper ......, Prentice-Hall Inc. NJ[8] Ning Hu, Randy K. Smith and Phillip G. Bradford "Security for Fixed Sensor Networks" ACMSE2004[9 ] S. Kumar and D. Shephered, “SenseIT: Sensor information technology for the warfighter,” in Proceedings of the 4th International Conference on Information Fusion, 2001 [10] Mike Chen, Weidong Cui, Victor Wen, and Alec Woo, “Security and Implementation Issues in a Sensor Network", 2000, UC Berkeley[11] Bruce Schneier, August 2004 "Olympic Security" online. [Available]http://smh.com.au/articles/2004/08/25/1093246605489.html [Accessed 28 August 2004][12] "10 emerging technologies that will change the world" online. [Available] http://et.its.psu.edu/public/news/tenETs2004.pdf [Accessed 28 August 2004]