Abstract: Wireless Sensor Network (WSN) is a special kind of ad-hoc network. WSNs are useful in many critical applications like military and surveillance, habitat monitoring, etc. Security has been a major concern in these networks due to restrictions of resources in the sensor nodes and less human intervention during its operation. This paper outlines the security requirements, threats and vulnerabilities in WSN operations and the associated existing works towards defending against malicious attacks..

Keywords: security threats, WSN , ad- hoc networks ,security requirements ,sensor nodes.