What does it do? smss.exe - This is the session manager subsystem, which is responsible for starting the user session. This process is initiated by the system thread and is responsible for various activities, including launching the Winlogon and Win32 (Csrss.exe) processes and setting system variables. After it has launched these processes, it waits for either Winlogon or Csrss to end. If this happens "normally," the system shuts down; if it happens unexpectedly, Smss.exe causes the system to stop responding (hang).
The smss.exe which is from Microsoft is located at c:\windows\System32\smss.exe . We've been able to find several viruses that run as smss to trick you.