Mobile Ad hoc NETwork (MANET) is one type of wireless network, which does not use infrastructure for establishing communication between the participating nodes in the network. Special characteristics of this network are to attract various types of attacks. This paper deals with wormhole attack, a type of Denial Of Service attack (DOS), which disrupts the network operation without performing functions in a genuine manner. This attack is formed by more than one malicious node and creates a virtual path between them. One of the attacker node tunnels the packets through this virtual path to the other attacker and that in turn retransmits the packet from there to reach the destination.