which event of system is raised when user logoff

using Microsoft.Win32;

 // you need to init this on service start
 SystemEvents.SessionEnding += 
            new SessionEndingEventHandler(SystemEvents_SessionEnding);


 void SystemEvents_SessionEnding(object sender, SessionEndingEventArgs e)
 {
     if (Environment.HasShutdownStarted)
     {
         //Handle shutdown
     }
     else
     {
         //Handle log off
     }
  }