The project "Störning av multisensorsystem" (Multisensor systems and countermeasures) has examined the effect of countermeasures on multisensor systems and how it may be possible to protect multisensor systems from countermeasures. The project has been running for two years with a separate pre-study during 2003. The result of the project is, above all, a tool for high quality simulation and verification of the effects of countermeasures on specific functions in sensors and sensor systems. The focus of the simulation platform is realism and signal quality, which is needed to handle ground scenarios reliably. The modularity that is given by using HLA-adapted components enables the use of specialized simulation programs for different parts in the system, e.g. specialized programs for radar and IR signal generation. This tool has been used to investigate the effect of countermeasures on target recognition and target tracking functions in a multisensor seeker.