Smss.exe
(Microsoft)
Windows NT4/2000/XP only. SMSS is the Session Manager SubSystem. SMSSs purpose is to start, manage, and delete user sessions (or client sessions under Terminal Server). Under Terminal Server the management part includes dealing with the different subsystems (OS/2, Win32, POSIX) which a client session may wish to run.
Recommendation :
An integral part of the operating system, leave alone.