Sensor networks enable application that connects the physical world to the virtual world.A wireless sensor network (WSN) consists of distributed autonomous sensors to closelymonitor physical or environmental conditions. Wireless platforms are less expensive andare more powerful, the applications supported by WSNs [1] vary from monitoring,tracking to controlling. In the era of interconnected world, security of both external andinternal data exchange over network nodes is a primary concern. This paper studies thesecurity issues within wireless sensor networks. A study of current threats in WSNs ismade and counter measures for them are being surveyed in this paper. In particular, theprotocol layer attack on sensor networks is being explored. Keywords: Wireless sensor network, security attacks, protocol layer attack
