  Wireless sensor networks have attracted a lot of interest over the last
decade in wireless and mobile computing research community. Applications of
these networks are numerous and growing, which range from indoor deployment
scenarios in the home and office to outdoor deployment in adversary's territory
in a tactical battleground. However, due to distributed nature and their
deployment in remote areas, these networks are vulnerable to numerous security
threats that can adversely affect their performance. This chapter provides a
comprehensive discussion on the state of the art in security technologies for
wireless sensor networks. It identifies various possible attacks at different
layers of the communication protocol stack in a typical sensor network and
their possible countermeasures. A brief discussion on the future direction of
research in WSN security is also included.
