How to prevent ALt+F4

[Latin4567]

im making a computer locking program which makes you enter a password to close it...

i need to prevent the user from pressing ALT + F4... I tried simply modifying the keypress event but it isnt working... why? do i need to use an api or somthing?

Private Sub TextBox1_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyDown, Me.KeyDown
        If e.KeyData = Keys.Enter Then
            e.SuppressKeyPress = True
            If TextBox1.Text = pas Then
                Me.Close()
            End If
        End If
 
        If e.Modifiers = Keys.Control + Keys.F4 Then
            e.SuppressKeyPress = True
        End If
    End Sub

[Latin4567]

oops.... replace keys.control with keys.alt.... (it still doesnt work, tho)

[Latin4567]

hmm.. well i fixed it by doing this:

If e.Alt Or e.Control Or e.KeyData = Keys.Delete = True Then
            e.SuppressKeyPress = True
            e.Handled = True
        End If

but how do i disable CTRL + ALT + DEL?

[RobDog888]

I may be wrong, but I have not seen any code that can do that yet. Its protected and it deals with the security dll - msgina.dll

Why do you need to prevent it? Maybe there is a workaround.

[Latin4567]

well im making a custom locked computer screen... i have sucessfully prevented alt f4.... but ctrl alt del still works

[Latin4567]

is it possible to do it via batch file or somthing?

[RobDog888]

I dont know but I have read a few posts about creating your own desktop for something like what your doing and try a search for them. I think they were creating their own explorer shellor something. Its easier and helps to contain everything in that shell.

[Latin4567]

ooh i figured it out....

i made a timer which sent the form to the front constantly, then i made a sub which gives it focus if it loses focus... so it goes in front of the task manager!

yay

[Phill64]

I have 'sort of' prevented ctrl+alt+del with an expirment or prototype for my last boss for a kiosk which was supposed be just a normal app but to lock out the user completely (assuming also they could not turn off the computer, not in same location as keyboard mouse etc)

i continously did this

Me.Show()
Me.SetTopLevel(True)
Me.Activate()

on the form, they r able to use ctrl+alt+del but it's rendered useless as they cant click anything on it, i cant remember but i did work out a few shortcut keys that still work in it

remember to use ctrl+pausebreak to end the project after you test this and don't run the exe

[Phill64]

Oh, you did the same thing anyway

[Latin4567]

ya, except mine doesnt flicker... you have to put a me.focus() under the formlostfocus event and then make a timer that does me.bringtofront()....
and it has to be a topmost form

[jo0ls]

disabletskmgr registry key. See article half way down this page:
http://www.devcity.net/newsletter/ar...ty20050715.htm

If you wanted to trap ctrl-alt-delete you would have to use msgina.dll, and you need to be able to use pointers properly (like in c++) - so you can't do it in c# or vb.net.

[RobDog888]

I thought someone could shed some light on this. Thanks for the link and I was right too about the msgina.dll.

[Latin4567]

well i have gotten it to work by forcing the window to always have focus and be ontop... so it goes ontop of the taskmanager rendering it useless... and i already disabled ALT+F4....
yay!

[TTn]

Imports System.Drawing
Imports System.Threading
Imports System.Reflection
Imports System.Runtime.InteropServices
Friend Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer. 
    'Do not modify it using the code editor.
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Button2 As System.Windows.Forms.Button

    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button
        Me.Button2 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(88, 72)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(128, 24)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Disable task manager."
        '
        'Button2
        '
        Me.Button2.Location = New System.Drawing.Point(88, 112)
        Me.Button2.Name = "Button2"
        Me.Button2.Size = New System.Drawing.Size(128, 24)
        Me.Button2.TabIndex = 2
        Me.Button2.Text = "Enable Task manager"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.Button2)
        Me.Controls.Add(Me.Button1)
        Me.Name = "Form1"
        Me.Text = "                 Ctrl + Alt + Delete"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Declare Function GetAsyncKeyState Lib "user32" (ByVal vKey As Integer) As Integer
    Public Declare Function UnhookWindowsHookEx Lib "user32" (ByVal hHook As Integer) As Integer
    Private Declare Sub keybd_event Lib "user32.dll" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Integer, ByVal dwExtraInfo As Integer)
    Private Declare Function CallNextHookEx Lib "user32" (ByVal hHook As Integer, ByVal nCode As Integer, ByVal wParam As Integer, ByVal lParam As KBDLLHOOKSTRUCT) As Integer
    Public Declare Function SetWindowsHookEx Lib "user32" Alias "SetWindowsHookExA" (ByVal idHook As Integer, ByVal lpfn As KeyboardHookDelegate, ByVal hmod As Integer, ByVal dwThreadId As Integer) As Integer

    Public Structure KBDLLHOOKSTRUCT
        Public vkCode As Integer
        Public scanCode As Integer
        Public flags As Integer
        Public time As Integer
        Public dwExtraInfo As Integer
    End Structure

    Public Delegate Function KeyboardHookDelegate(ByVal Code As Integer, ByVal wParam As Integer, ByRef lParam As KBDLLHOOKSTRUCT) As Integer
    <MarshalAs(UnmanagedType.FunctionPtr)> Private callback As KeyboardHookDelegate
    Public KeyboardHandle As Integer

    ' Low-Level Keyboard Constant
    Const HC_ACTION As Integer = 0

    ' Virtual Keys
    Const KEYEVENTF_KEYUP As Short = &H2
    Const VK_SHIFT As Integer = &H10
    Const VK_CONTROL = &H11
    Const VK_DELETE = &H2E
    Const VK_MENU = &H12
    Const VK_ESCAPE As Integer = &H1B
    Const WH_KEYBOARD_LL As Integer = 13&


    'This function allows keys to be detected and dealt with.
    Public Function IsHooked(ByRef Hookstruct As KBDLLHOOKSTRUCT) As Boolean
        On Error Resume Next

        ' ctrl alt delete, can be detected here. The task manager is closed.
        If (Hookstruct.vkCode = VK_DELETE) And CBool(GetAsyncKeyState(VK_MENU) And &H8000) And CBool(GetAsyncKeyState(VK_CONTROL) And &H8000) Then
            Do
                Application.DoEvents()
                SendKeys.Flush()
                Dim clt() As Process = Process.GetProcessesByName("taskmgr")
                For Each p As Process In clt

                    'kill task manager and rip from memory
                    p.Kill()

                    'Thanks to Dan Appleman, who doesn't know why either.
                    Application.DoEvents()
                    SendKeys.Flush()

                    'Return Task Manager function here, to replace memory.
                    'Simulate Ctrl Shift Esc to call task managers back to duty.
                    keybd_event(VK_CONTROL, 0, 0, 0)
                    keybd_event(VK_SHIFT, 0, 0, 0)
                    keybd_event(VK_ESCAPE, 0, 0, 0)
                    keybd_event(VK_ESCAPE, 0, KEYEVENTF_KEYUP, 0)
                    keybd_event(VK_SHIFT, 0, KEYEVENTF_KEYUP, 0)
                    keybd_event(VK_CONTROL, 0, KEYEVENTF_KEYUP, 0)
                    'END--Ctrl Alt Delete has been essentially blocked here from bringing up the task manager.
                    'If you want to personalize your own application's task manager.
                    'Call MyTaskMangerReplacement(1) 
                    Application.DoEvents()
                    SendKeys.Flush()
                    Exit Do
                Next
                Application.DoEvents()
                SendKeys.Flush()
            Loop
        End If

        'disable task manager for, control shift esc.
        If (Hookstruct.vkCode = VK_ESCAPE) And CBool(GetAsyncKeyState(VK_CONTROL) And &H8000) And CBool(GetAsyncKeyState(VK_SHIFT) And &H8000) Then
            Return True
        End If

        Return False
    End Function

    'Call this to hook keyboard
    Public Sub HookKeyboard()
        callback = New KeyboardHookDelegate(AddressOf KeyboardCallback)
        KeyboardHandle = SetWindowsHookEx(WH_KEYBOARD_LL, callback, Marshal.GetHINSTANCE([Assembly].GetExecutingAssembly.GetModules()(0)).ToInt32, 0)
    End Sub

    ' UnhookKeyboard is very important to include in the form's unload.
    Public Sub UnhookKeyboard()
        If (Hooked()) Then
            Call UnhookWindowsHookEx(KeyboardHandle)
        End If
    End Sub

    'Indicates hook success.
    Private Function Hooked()
        Hooked = KeyboardHandle <> 0
    End Function

    Public Function KeyboardCallback(ByVal Code As Integer, ByVal wParam As Integer, ByRef lParam As KBDLLHOOKSTRUCT) As Integer
        If (Code = HC_ACTION) Then
            If (IsHooked(lParam)) Then
                Return 1
            End If
        End If
        Return CallNextHookEx(KeyboardHandle, Code, wParam, lParam)
    End Function

    Private Sub Form1_Closed(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Closed
        On Error Resume Next

        'unhook keyboard control
        UnhookKeyboard()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        HookKeyboard()
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        On Error Resume Next
        UnhookKeyboard()
    End Sub
End Class

[ahostbr]

this is probably the most malicious piece of code if ever wrote...
but it will do what you asked... in vista and in XP

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Me.BringToFront()
        Me.Focus()
        Me.TopMost = True
        Me.Show()
        Me.SetTopLevel(True)
        Me.Activate()
        Me.WindowState = FormWindowState.Maximized
        Try
            killProcess("LogonUI")
            killProcess("taskmgr")
        Catch ex As Exception
            Return
        End Try
    End Sub
 
    Public Sub killProcess(ByRef strProcessToKill As String)
        Try
            Dim proc() As Process = Process.GetProcesses
            For i As Integer = 0 To proc.GetUpperBound(0)
                If proc(i).ProcessName = strProcessToKill Then
                    proc(i).Kill()
                End If
            Next
        Catch ex As Exception
            Return
        End Try
   
    End Sub

[Kasracer]

All of these methods are terrible and will not work if the computer is part of a domain (and thus, CTRL + ALT + DEL jumps to the management screen) or has a sane security policy.

If you're making a kiosk system you really should not use a consumer or server OS; you should be using an embedded OS (like Windows CE 6). If you're making some sort of locking screen... we'll you're just duplicating OS functionality and since it's not low level enough it means you'll be able to break it in one way or another despite what you do.

Also, killing processes is very bad. Especially if you're doing it by name as I could have a process called LogonUI that you're application is now killing rather than its true target. Let's not forget that you can't just kill random processes in Vista unless you have the appropriate security level.

Why was this thread dug from the grave anyway?

[wiz....]

Hey Latin4567 !!!!! can u please post the project so that curious people like me can try it out????????

thanking you in advance,
wiz....

[wiz....]

hey latin4567 !!!!can u post the project for dummies like me????

thanks in advance,
wiz....