This is the user-mode portion of the Win32 subsystem (with Win32.sys being the kernel-mode portion). Csrss stands for client/server run-time subsystem and is an essential subsystem that must be running at all times. Csrss is responsible for console windows, creating and/or deleting threads, and some parts of the 16-bit virtual MS-DOS environment.
Note: The csrss.exe file is located in the c:\windows\System32 folder. In other cases, csrss.exe is a virus, spyware, trojan or worm!
(from the link below:)
http://www.neuber.com/taskmanager/process/.../csrss.exe.htmlIt could be time to scan for viruses.