The program Csrss.exe is technically referred to as Client / Server Runtime Subsystem. It is a valid program of the Microsoft Windows NT OS. It runs using user-mode of the Win32 subsystem. This program is incorporated in various Microsoft environment such as Windows 2003 and 2000, Windows Vista and XP, and Server 2008 & 7.

In most operating systems, the Win32 subsystems operations had been transferred in to the kernel mode drivers. In newer operating systems such as in Windows NT 4 environment, the Csrss.exe program is responsible for the GUI (Graphical User Interface) shutdown, threading and Win32 console windows.

Given the background of the program Csrss.exe mentioned above, it is considered as a crucial process to system operations. This means that ones you terminate the said program, your computer will most probably experience system failure. Because it is a critical program, under the usual circumstances, Csrss.exe cannot be disabled or terminated using any of the task skill commands or even if you terminate the program using the Windows Task Manager. Although there is an exception, if you are running Task Manager on Windows Vista with an Administrator access, then you can terminate Csrss.exe. If you are using Windows 7, the Task Manager gives you the user caution that once the process is terminated, the end result would be a system failure. Users have the option to continue terminating the program or not.

Csrss.exe is utilized using a system service on user-mode. If such process calls out a command from Win32 subsystem, Win32 libraries (gdi32.dll & user32.dll) will send out an interprocess call instead of a system call. The work will then be done by the program without the kernel being compromised.

On Windows NT 3.x, it has transferred the Graphic Device Interface element of the Csrss program to kernel mode. In Windows NT 4.0 such change created an improved and enhanced graphic visuals and performance.

Although the Csrss.exe is a legitimate process, there are many computer threats such as trojans, viruses and spyware that conceal themselves as the Csrss program. Most of the known virus programs are Nimda. E, W32/ Netsky.ab@MM and W32/ VBMania@MM, among others.

If you are running an anti-virus software on your computer and it labels the program to be a malware or any other computer threat, you can use an anti-virus software to determine if the Csrss.exe program is harmful to your system.