A Mobile Ad hoc NETwork (MANET) is a self-organized wireless short-lived network consisting of mobile nodes. The mobile nodes communicate with one another by wireless radio links without the use of any pre-established fixed communication network infrastructure. The mobile nodes are vulnerable to different types of security attacks that allow interception, injection, and interference of communication among nodes. Possible damages include leaking secret information, message contamination and node impersonation. MANETs need secure routing protocols to prevent possible security attacks.