In this article, we propose a fault-tolerant and grid-based IDS, named Fault-tolerant Grid Intrusion Detection System (FGIDS) which exploits grid?s dynamic and abundant computing resources to detect malicious behaviors from a massive amount of network packets. In FGIDS, a detector can dynamically leave or join FGIDS anytime. A newly joined one is tested to obtain its key features? performance curves, which are used to balance detection workload among detectors. When a detector due to some reasons can not continue its detection leaving an unfinished task, FGIDS allocates another available one to take over. Therefore the drawbacks ordinary security systems have experienced can be then eliminated.