Mobile ad hoc network is a type of self configurable, dynamic wireless network in which all the mobile devices are connected to one another without any centralized infrastructure. Since, the network topology of MANETs changes rapidly. It is vulnerable to routing attacks than any other infrastructure based wireless and wired networks. Hence, providing security to this infrastructure-less network is a major issue. This paper investigates on the security mechanisms that are proposed for Selfish node attack, Shared root node attack and the Control packet attack in MANETs with the aid of a well known multicast routing protocol namely Multicast Ad-hoc On-demand Distance Vector (MAODV).