An ad hoc network is a collection of wireless mobile nodes that forms a temporary network without any centralized administration. While early research effort assumed a friendly and cooperative environment and focused on problems such as wireless channel access and multihop routing, security has become a primary concern in order to provide protected communication between nodes in a potentially hostile environment. Recent wireless research indicates that the wireless MANET presents a larger security problem than conventional wired and wireless networks. Distributed Denial of Service (DDoS) attacks have also become a problem for users of computer systems connected to the Internet. A DDoS attack is a distributed, large-scale attempt by malicious users to flood the victim network with an enormous number of packets. This exhausts the victim network of resources such as bandwidth, computing power, etc. The victim is unable to provide services to its legitimate clients and network performance is greatly deteriorated. In this paper, we have studied the vulnerability of MANETs to DDoS attacks and provide an overview of detection and prevention of DDoS attacks in MANET (Mobile Ad hoc Network).