Sperrung des Computers erkennen - Visual Basic 6

Declare Function CallWindowProc Lib "user32" Alias _  
    "CallWindowProcA" (ByVal lpPrevWndFunc As Long, _  
    ByVal hWnd As Long, ByVal MSG As Long, _
    ByVal wParam As Long, ByVal lParam As Long) As Long

Declare Function SetWindowLong Lib "user32" Alias _  
    "SetWindowLongA" (ByVal hWnd As Long, _  
    ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

Public Declare Function WTSRegisterSessionNotificationA Lib "WtsApi32.dll" Alias _  
    "WTSRegisterSessionNotification" (ByVal hWnd As Long, ByVal dwFlags As Long) As Long  
    
Public Declare Function WTSUnRegisterSessionNotificationA Lib "WtsApi32.dll" Alias _  
    "WTSUnRegisterSessionNotification" (ByVal hWnd As Long) As Long  
    
Private Const GWL_WNDPROC As Long = -4&
Private Const WM_WTSSESSION_CHANGE As Long = &H2B1
Private Const WTS_SESSION_LOCK As Long = 7
Private Const WTS_SESSION_UNLOCK As Long = 8
Public Const WTS_SESSION_LOGON As Long = 5
Public Const WTS_SESSION_LOGOFF As Long = 6
Private Const NOTIFY_FOR_THIS_SESSION As Long = &H0

Private gHW As Long
Private lpPrevWndProc As Long

Public Sub Hook(hWnd As Long)
    gHW = hWnd
    lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, AddressOf WindowProc)
    Call WTSRegisterSessionNotificationA(hWnd, NOTIFY_FOR_ALL_SESSIONS)
End Sub

Public Sub Unhook()
    Call SetWindowLong(gHW, GWL_WNDPROC, lpPrevWndProc)
    Call WTSUnRegisterSessionNotificationA(gHW)
End Sub

Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, _
    ByVal wParam As Long, ByVal lParam As Long) As Long
    
    Select Case uMsg
      Case WM_WTSSESSION_CHANGE
        Select Case wParam
          Case WTS_SESSION_LOCK
            'Sitzuung wird gesperrt  
              '...  
          Case WTS_SESSION_UNLOCK
            'Sitzung wird entsperrt  
              '...  
        End Select
    End Select
      'Auf jeden Fall die Standardverarbeitung aufrufen  
    WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, lParam)
End Function