Desabilitar as teclas ctrl+alt+del.

Procedure TForm1.Button1Click(Sender: TObject);
Var
numero: integer;
begin
SystemParametersInfo(97,Word(true),@numero,0);
end;
{habilita}
procedure TForm1.Button2Click(Sender: TObject);
Var
numero: integer;
begin
SystemParametersInfo(97,Word(false),@numero,0);
end;