Blocking User Interaction in WinForms (C#)

blocker.cs

using Microsoft.Win32;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace VPZ.Security
{

    public class Blocker
    {

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr CallNextHookEx(IntPtr hook, int nCode, IntPtr wp, IntPtr lp);
        [DllImport("user32")]
        private static extern bool DeleteMenu(int Menu, int Position, int Flags);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern int FindWindow(string Class, string Text);
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        private static extern short GetAsyncKeyState(Keys key);
        [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetModuleHandle(string name);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern int GetSystemMenu(IntPtr Handle, bool Revert);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr SetWindowsHookEx(int id, LowLevelKeyboardProc callback, IntPtr hMod, uint dwThreadId);
        [DllImport("user32.dll")]
        private static extern int ShowWindow(int Handle, int Command);
        private delegate IntPtr LowLevelKeyboardProc(int nCode, IntPtr wParam, IntPtr lParam);
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool UnhookWindowsHookEx(IntPtr hook);
        [StructLayout(LayoutKind.Sequential)]
        private struct KBDLLHOOKSTRUCT
        {
            public Keys Key;
            public int Code;
            public int Flags;
            public int Time;
            public IntPtr Extra;
        }

        private IntPtr Handle;
        private IntPtr Hook;
        private LowLevelKeyboardProc Process;
        private const String SYSTEM_REGISTRY_KEY = "Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
        private const int SYSTEM_WINDOW_HIDE = 0;
        private const int SYSTEM_WINDOW_SHOW = 1;

        public Blocker(IntPtr Handle)
        {
            this.Handle = Handle;
        }

        private IntPtr CaptureKey(int Code, IntPtr Window, IntPtr Process)
        {
            if (Code >= 0)
            {
                bool Suppress = false;
                KBDLLHOOKSTRUCT Key = (KBDLLHOOKSTRUCT)Marshal.PtrToStructure(Process, typeof(KBDLLHOOKSTRUCT));
                if ((Key.Key == Keys.Escape && ((Key.Flags & 0x20) == 0x20)))
                    Suppress = true;
                if ((Key.Key == Keys.Escape) && ((Control.ModifierKeys & Keys.Control) == Keys.Control))
                    Suppress = true;
                if ((Key.Key == Keys.F4 && ((Key.Flags & 0x20) == 0x20)))
                    Suppress = true;
                if ((Key.Key == Keys.Tab && ((Key.Flags & 0x20) == 0x20)))
                    Suppress = true;
                if ((Key.Key == Keys.LWin) || (Key.Key == Keys.RWin))
                    Suppress = true;
                if (Suppress)
                    return (IntPtr)1;
            }
            return CallNextHookEx(Hook, Code, Window, Process);
        }

        public void DisableCloseButton()
        {
            DeleteMenu(GetSystemMenu(this.Handle, false), 6, 1024);
        }

        public void DisableSpecialKeys()
        {
            ProcessModule Module = System.Diagnostics.Process.GetCurrentProcess().MainModule;
            Process = new LowLevelKeyboardProc(CaptureKey);
            Hook = SetWindowsHookEx(13, Process, GetModuleHandle(Module.ModuleName), 0);
        }

        public void DisableTaskBar()
        {
            ShowWindow(FindWindow("Shell_TrayWnd", ""), SYSTEM_WINDOW_HIDE);
        }

        public void DisableTaskManager()
        {
            RegistryKey Root = null;
            try
            {
                Root = Registry.CurrentUser.CreateSubKey(SYSTEM_REGISTRY_KEY);
                Root.SetValue("DisableTaskMgr", "1");
            }
            catch (Exception Error)
            { }
            finally
            {
                if (Root != null)
                {
                    try
                    {
                        Root.Close();
                    }
                    catch (Exception Error)
                    { }
                }
            }
        }

        public void EnableCloseButton()
        {
            DeleteMenu(GetSystemMenu(this.Handle, true), 6, 1024);
        }

        public void EnableSpecialKeys()
        {
            UnhookWindowsHookEx(Hook);
        }

        public void EnableTaskBar()
        {
            ShowWindow(FindWindow("Shell_TrayWnd", ""), SYSTEM_WINDOW_SHOW);
        }

        public void EnableTaskManager()
        {
            RegistryKey Root = null;
            try
            {
                Root = Registry.CurrentUser;
                RegistryKey Sub = Root.OpenSubKey(SYSTEM_REGISTRY_KEY);
                if (Sub != null)
                    Root.DeleteSubKeyTree(SYSTEM_REGISTRY_KEY);
            }
            catch (Exception Error)
            { }
            finally
            {
                if (Root != null)
                {
                    try
                    {
                        Root.Close();
                    }
                    catch (Exception Error)
                    { }
                }
            }
        }

    }

}

demo.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;

namespace VPZ.Security
{

    public partial class Demo : Form
    {

        private Blocker Blocker;
        private Form Overlay;

        public Demo()
        {
            this.InitializeComponent();
            this.Blocker = new Blocker(this.Handle);
        }

        private void Block()
        {
            this.Blocker.DisableCloseButton();
            this.Blocker.DisableSpecialKeys();
            this.Blocker.DisableTaskBar();
            this.Blocker.DisableTaskManager();
            // This overlay prevents mouse-clicks
            this.Overlay = new Form()
            {
                BackColor = Color.Black,
                FormBorderStyle = FormBorderStyle.None,
                Opacity = 0.5,
                WindowState = FormWindowState.Maximized
            };
            this.Overlay.Show();
        }

        private void OnNegativeClick(object Sender, EventArgs Event)
        {
            this.Unblock();
            ((Button)Sender).Enabled = false;
            this.Positive.Enabled = true;
        }

        private void OnPositiveClick(object Sender, EventArgs Event)
        {
            this.Block();
            ((Button)Sender).Enabled = false;
            this.Negative.Enabled = true;
        }

        private void Unblock()
        {
            this.Blocker.EnableCloseButton();
            this.Blocker.EnableSpecialKeys();
            this.Blocker.EnableTaskBar();
            this.Blocker.EnableTaskManager();
            this.Overlay.Close();
        }

    }

}