Mencegah Alt+F4

public

procedure AppMessage(var Msg: TMSG; var HAndled: Boolean);
end;
{...}
implementation
{...}

procedure TForm1.FormCreate(Sender: TObject);
begin
Application.OnMessage := AppMessage;
end;

procedure TForm1.AppMessage(var Msg: TMSG; var Handled: Boolean);
begin
Handled := False;
case Msg.Message of
WM_SYSKEYDOWN:
if Msg.wParam = VK_F4 then
Handled := True; // don't allow ALT-F4
end;
end;