F-Secure anti-virus products don't detect any virus by this name. However, the FS 'virus' is a special marker built in to VIRSTOP. Basically, if VIRSTOP reports FS virus, it means that VIRSTOP is not working correctly. Contact F-Secure anti-virus support for more information.
Allow F-Secure Anti-Virus to disinfect the relevant files.
For more general information on disinfection, please see Removal Instructions.