Bold text in MessageBox

It is possible, a message box is a regular window that can be messed with like any other. The code to do so is however a bit gritty. Add a new class to your project and paste this code:

using System;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;

class BoldMessageBox : IDisposable {
  private int mTries = 0;
  private Form mOwner;
  private Font mFont;

  public BoldMessageBox(Form owner) {
    mOwner = owner;
    owner.BeginInvoke(new MethodInvoker(findDialog));
  }

  private void findDialog() {
    // Enumerate windows to find the message box
    if (mTries < 0) return;
    EnumThreadWndProc callback = new EnumThreadWndProc(checkWindow);
    if (EnumThreadWindows(GetCurrentThreadId(), callback, IntPtr.Zero)) {
      if (++mTries < 10) mOwner.BeginInvoke(new MethodInvoker(findDialog));
    }
  }
  private bool checkWindow(IntPtr hWnd, IntPtr lp) {
    // Checks if <hWnd> is a dialog
    StringBuilder sb = new StringBuilder(260);
    GetClassName(hWnd, sb, sb.Capacity);
    if (sb.ToString() != "#32770") return true;
    // Got it, get the STATIC control that displays the text
    IntPtr hText = GetDlgItem(hWnd, 0xffff);
    if (hText != IntPtr.Zero) {
      // Get the current font
      IntPtr hFont = SendMessage(hText, WM_GETFONT, IntPtr.Zero, IntPtr.Zero);
      Font font = Font.FromHfont(hFont);
      // And make it bold (note the size change to keep enough space!!)
      mFont = new Font(font.FontFamily, font.SizeInPoints - 1f, FontStyle.Bold);
      SendMessage(hText, WM_SETFONT, mFont.ToHfont(), (IntPtr)1);
    }
    // Done
    return false;
  }
  public void Dispose() {
    mTries = -1;
    mOwner = null;
    if (mFont != null) mFont.Dispose();
  }

  // P/Invoke declarations
  private const int WM_SETFONT = 0x30;
  private const int WM_GETFONT = 0x31;
  private delegate bool EnumThreadWndProc(IntPtr hWnd, IntPtr lp);
  [DllImport("user32.dll")]
  private static extern bool EnumThreadWindows(int tid, EnumThreadWndProc callback, IntPtr lp);
  [DllImport("kernel32.dll")]
  private static extern int GetCurrentThreadId();
  [DllImport("user32.dll")]
  private static extern int GetClassName(IntPtr hWnd, StringBuilder buffer, int buflen);
  [DllImport("user32.dll")]
  private static extern IntPtr GetDlgItem(IntPtr hWnd, int item);
  [DllImport("user32.dll")]
  private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
}

And use it like this:

private void button1_Click(object sender, EventArgs e) {
  using (new BoldMessageBox(this)) {
    MessageBox.Show("Nobugz waz here");
  }
}

There is one flaw in this approach. After making the font bold, the text must still fit in the static control that the message box reserved for the text. That required me to make the font smaller. You may have to tweak this value.