I PASJ I nternational Journal of E lectronics & Communication (I I JE C) Web Site: http://www.ipasj.org/IIJEC/IIJEC.htm A Publisher for Research Motivatin........ Email: editoriijec@ipasj.org Volume 2, Issue 1, January 2014 ISSN 2321-5984 Volume 2, Issue 1, January 2014 Page 16 ABSTRACT A wireless sensor network (WSN) is comprised of a large number of sensors that collaboratively monitor various environments. The sensors all together provide global views of the environments that offer more information than those local views provided by independently operating sensors. There are numerous potential applications of WSNs in various areas such as residence, industry, military and many others. While the deployment of sensor nodes in an unattended environment makes the networks vulnerable to a variety of potential attacks. This paper focuses the various attacks associated with wireless sensor network. Key words: Wireless sensor network, Sybil attack, Wormhole attack, Sinkhole attack, Hello flood attack. 1. INTRODUCTION Wireless sensor Networks (WSN) consists of protocols and algorithms with self- organizing capabilities. It is used for monitoring large areas of spatial and temporal regions [1]. They are the networks that consist of sensors for sensing temperature, pressure and humidity that are distributed in an adhoc manner. The following are some factors which influence the design of sensor networks: Fault tolerance, scalability, production cost, operating environment, hardware constraints, power consumption and transmission media [2]. These sensors are of low cost, limited memory and energy is constrained due to their smaller size. They work with each other to sense some physical phenomenon. The gathered information is processed to get relevant results. An example of WSN is depicted in figure 1.Any physical quantity can be monitored by using a wireless device with a sensor and networking these sensors with the help of wireless communication capability. The advancement in WSN increases the life time of the nodes, but node failure is expected due to limited energy budget, environmental degradation, mechanical/electrical problems or battery depletion. This failure of nodes is true for sensor networks implemented in dangerous and critical applications like forest fire and defense applications. Figure 1: Wireless Senor Network Architecture Sensor networks are widely used in both army and civil services such as battlefield surveillance, medical observation, ATTACKS AND COUNTERMEASURES IN WSN J.Steffi Agino Priyanka 1 , S.Tephillah 2 and A.M.Balamurugan 3 1 PG Scholar, St. Joseph’s College of Engineering, Chennai, Tamil Nadu 2 SAssociate Professor, St. Joseph’s College of Engineering, Chennai, Tamil Nadu 3 Associate Professor, St. Joseph’s College of Engineering, Chennai, Tamil Nadu