The emergence of sensor networks as one of the dominant technology trends in the coming decades has
posed numerous unique challenges to researchers. These networks are likely to be composed of hundreds,
and potentially thousands of tiny sensor nodes, functioning autonomously, and in many cases, without
access to renewable energy resources. Cost constraints and the need for ubiquitous, invisible
deployments will result in small sized, resource-constrained sensor nodes. While the set of challenges in
sensor networks are diverse, we focus on security of Wireless Sensor Network in this paper. We propose
some of the security goal for Wireless Sensor Network. Further, security being vital to the acceptance and
use of sensor networks for many applications; we have made an in depth threat analysis of Wireless
Sensor Network. We also propose some countermeasures against these threats in Wireless Sensor
Network.