isass.exe is registered as the Optix.Pro virus which carries the ability to disable firewalls and local security protections, and a backdoor capability in its payload.
Non-system processes like isass.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you
check your registry to identify slowdown issues.