All of the previously mentioned security threats, the Hello flood
attack, wormhole attack, Sybil attack, sinkhole attack, serve one
common purpose that is to compromise the integrity of the
network they attack. Also In the past, focus has not been on the
security of WSNs, but with the various threats arising and the
importance of data confidentiality, security has become a major
issue. Although some solutions have already been proposed,
there is no single solution to protect against every threat. In our
paper we mainly focus on the security threats in WSN. We‟ve
presented the summery of the WSNs threats affecting different
layers along with their defense mechanism. We conclude that the
defense mechanism presented just gives guidelines about the
WSN security threats; the exact solution depends on the type of
application the WSN is deployed for. There‟re many security
mechanisms which are used in „layer-by-layer‟ basis as a security
tool. Recently researchers are going for integrated system for
security mechanism instead of concentrating on different layers
independently. Through this paper we‟ve tried to present the
most common security threats in various layers and their most
probable solution.