How To Block CTRL+ALT+DEL and ALT+TAB in Windows 95 or Windows 98

MORE INFORMATION

Sometimes it is necessary for a program to prevent the use of the CTRL+ALT+DEL key combination to open the Close Program task list to end a task or shut down Windows 95, Windows 98, or Windows Me and to prevent the use of the ALT+TAB key combination to switch tasks. The following technique uses the SystemParametersInfo API to trick Windows 95, Windows 98, or Windows Me into thinking that a screen saver is running. As a side effect, CTRL+ALT+DEL and ALT+TAB are disabled.

The Win32 SDK states:

Note that disabling CTRL+ALT+DEL is not recommended because the Close Program dialog box was created to enable users to terminate misbehaving applications. If a program "hangs" while CTRL+ALT+DEL is disabled, it may not be possible to terminate it by any method other than rebooting the computer, which could result in the loss of data. Also, this technique may not work in future versions of Windows.

Step-by-Step Example

1. Start a new Standard EXE project. Form1 is created by default.
2. Add two CommandButton controls (Command1 and Command2) to Form1.
3. Add the following code to the General Declarations section of Form1:

         Private Const SPI_SCREENSAVERRUNNING = 97&
         Private Declare Function SystemParametersInfo Lib "User32" _
             Alias "SystemParametersInfoA" _
            (ByVal uAction As Long, _
             ByVal uParam As Long, _
             lpvParam As Any, _
             ByVal fuWinIni As Long) As Long
   
         Private Sub Form_Load()
            Command1.Caption = "Disabled"
            Command2.Caption = "Enabled"
         End Sub
   
         Private Sub Form_Unload(Cancel As Integer)
            'Re-enable CTRL+ALT+DEL and ALT+TAB before the program terminates.
            Command2_Click
         End Sub
   
         Private Sub Command1_Click()
            Dim lngRet As Long
            Dim blnOld As Boolean
            lngRet = SystemParametersInfo(SPI_SCREENSAVERRUNNING, True, _
            blnOld, _
               0&)
         End Sub
   
         Private Sub Command2_Click()
           Dim lngRet As Long
           Dim blnOld As Boolean
           lngRet = SystemParametersInfo(SPI_SCREENSAVERRUNNING, False, _
           blnOld, _
              0&)
         End Sub
   
   					

4. Press the F5 key to run the program, and then click the "Disabled" button. CTRL+ALT+DEL and ALT+TAB are disabled. Click the "Enabled" button to enable CTRL+ALT+DEL and ALT+TAB again.