Maintaining Security in the wireless networks is a major concern of issue in todays era. Many approaches are suggested and implemented such as VPN, Personal Area networks and Firewall.But each of the techniques have some or other issues due to which it wont be called as effective and efficient technique. In wireless network, security is not only done within the connections over the network, but its also important to do on the nodes separately. The networks and the nodes must be monitored for the particular set of selected metrics and on the basis of it, further actions can be planned for it. Nodes can behave in malicious manner and disturb the working of the network. This paper covers the vulnerabilities in the wireless ad hoc mobile network due to which malicious nodes effect the network. It also highlights the major preventive mechanisms that have been developed to avoid the malicious nodes.