Abstract: In this study, we present our experience in developing a tool for Software-Implement Fault Injection (SWIFI) into Windows operation system. The fault injector uses software-base strategies to emulate the effects of radiation-induced transients occurring in the system hardware components. The SWIFI tool called MOFI (Memory Oriented Fault Injector) is being used, in conjunction with an appropriate system fault model, to evaluate the applications, measure the injecting strength of injector and mean time to failure of injected applications and determine the sensitivity of applications to faults. The MOFI has been validated to inject faults into user-specified CPU registers and memory regions with many random distributions in location and uniform random distribution in time. The different random distributions chosen in location could produce different experiment results. The reason will be discussed in this study.