HOWTO: Block CTRL+ALT+DEL and ALT+TAB in Windows 95

• Learning, Professional, and Enterprise Editions of Microsoft Visual Basic for Windows, version 5.0
• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 32-bit only, for Windows, version 4.0

WARNING: ANY USE OF THE CODE PROVIDED IN THIS ARTICLE IS AT YOUR OWN RISK. Microsoft provides this code "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of merchantability and/or fitness for a particular purpose.

SUMMARY

You can prevent the CTRL+ALT+DEL and ALT+TAB key combinations from bringing up a task list in Windows 95 by calling the SystemParametersInfo function in the Win32 API. A step-by-step example of this appears below.

NOTE: This is possible only in Windows 95.

MORE INFORMATION

Sometimes it is necessary for a program to prevent the use of the CTRL+ALT+DEL key combination to bring up the Close Program task list to end a task or shut down Windows 95 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 into thinking that a screen saver is running. As a side effect, CTRL+ALT+DEL and ALT+TAB are disabled.

The Win32 SDK states:

   "SPI_SCREENSAVERRUNNING Windows 95: Used internally; applications should
   not use this flag. Windows NT: Not supported."

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 Form1's General Declarations section:

         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 click the "Disabled" CommandButton. CTRL+ALT+DEL and ALT+TAB are disabled. Click the "Enabled" CommandButton to enable CTRL+ALT+DEL and ALT+TAB again.

REFERENCES

Microsoft Developer Network CD (A subscription to the Microsoft Developer Network may be purchased from Microsoft. For more information on this product call (800)759-5474 in the U.S. and Canada.)