Wireless sensor networks are vulnerable to security attacks due to their unattended nature and deployment in hostile environment. Security attacks include false data injection, data forgery and eavesdropping. Adversaries can inject false data reports into the WSN through compromised nodes. The compromised nodes distort data integrity by injecting false data during data forwarding. The injected false data reports lead the en-route nodes and the base station to make false decision. Moreover, false decision depletes the energy of en-route nodes and the base station and creates threat to the lifetime of the sensor nodes. To detect and drop false data number of en-route filtering schemes have been developed.