In this paper, the authors analyze the black hole attack and its prevention in Mobile Ad-hoc NETwork (MANET). In this attack, a malicious node falsely advertises good path to the destination node during the path-finding process or in the route update message. By doing this, the malicious node dropped all the data packets from the source node. They propose a trusted vector based detection scheme. To simulate Black Hole attacks, a new Black Hole protocol is added into AODV Protocol. A new AODV protocol using C++ is written, to simulate the Black Hole attack. The effectiveness of the proposed technique depends on the selection of threshold values. In order to test the proposed method, a simulation model was developed.