DOCUMENT:Q161133 21-MAR-1997 [vbwin] TITLE :HOWTO: Block CTRL+ALT+DEL and ALT+TAB in Windows 95 PRODUCT :Microsoft Visual Basic for Windows PROD/VER:5.0 OPER/SYS:WINDOWS KEYWORDS:kbenv vb5all vb5howto VBKBEnv VBKBProgramming VBKBWinAPI kbhowto ====================================================================== --------------------------------------------------------------------- The information in this article applies to: - Learning, Professional, and Enterprise Editions of Microsoft Visual Basic for Windows, version 5.0 --------------------------------------------------------------------- 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." 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 machine, 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 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.) Additional query words: reboot ====================================================================== Keywords : kbenv vb5all vb5howto VBKBEnv VBKBProgramming VBKBWinAPI kbhowto Version : 5.0 Platform : WINDOWS Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 1997.