Most of the attacks in wireless sensor networks arecaused by the insertion of false information.
For defending the inclusion of false reports by compromised nodes is required detecting
mechanism. Developing such detection mechanism is great research challenge. All of the
previously mentioned security threats i.e the HELLO flood attack, wormhole attack, sinkhole
attack, Sybil attack serves one common purpose thatis to compromise the integrity of the network
they attack. In the past focus has not been on the security of WSNs. Security has become a major
issue for data confidentiality as the various threats are arising. In this paper we have tried to
present most of the security threats in WSN with extensive study.