Availability of services in a Grid Computing system is a security concerned that has received enormous attention in the recent years. Distributed Denial of Service attack (DDoS) is one of the major threats to Grid Computing services. This project presents vulnerability of Grid Computing in presence of DDoS attack. Our proposed method is based upon DDoS attack detection and recovery which uses a Game Theory to detect DDoS attack and also designing a Trust Based Model in detecting a DDoS attack and comparing the above two models.