Csrss.exe
(Microsoft)
Windows NT4//2000/XP only. CSRSS is the Client Server Runtime SubSystem. CSRSS is started by SMSS. When the user application makes a Win32 API call, it is usually CSRSS which communicates with the operating systems Kernel to execute the API call. CSRSS is also known as the Win32 Subsystem.
Recommendation :
An integral part of the operating system, leave alone.