Emmanuel Siqueira,
Você pode colocar isso:
if (e.KeyCode == Keys.Tab || e.Alt) e.SuppressKeyPress = true;
Mas... veja também:
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Disable Alt + Tab in C# program
Code Block
//using System.Runtime.InteropServices;
[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool SetForegroundWindow(IntPtr hWnd);
//Timer object's tick event
private void timer1_Tick(object sender, EventArgs e)
{
SetForegroundWindow(this.Handle);
}
https://social.msdn.microsoft.com/Forums/vstudio/en-US/d15600ee-150c-4a4f-b50f-71187de3bf94/disable-alt-tab-in-c-program
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How do disable the Alt+Tab,Alt+F4,ctr+Alt+Delete buttons from C# program? [closed]
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=1165450&SiteID=1
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[]'s,
Fabio I.