The traditional notion of a Adhoc wireless network is one in which there are a few Base Stations or Access Points and a number of Mobile Stations or Nodes. Security has become a primary concern in order to provide protected communication between mobile nodes in a hostile environment. The Adhoc networks pose a number of nontrivial challenges to security design, such as open peer-to-peer network architecture, shared wireless medium and network topology. These challenges clearly make a case for building multifence security solutions that achieve both road protection and desirable network performance. The general security objectives like authentication, confidentiality, integrity, availability and non-repudiation, the ad hoc routing protocols should also address location confidentiality, cooperation fairness and absence of traffic diversion. In this paper we attempt to analyze Challenges, Overview of Security, attacks, threats faced by the Adhoc network environment and provide a classification of the various security mechanisms.