Как узнать, подключен ли компьютер к сети?

procedure TForm1.Button1Click(Sender: TObject); 
begin 
  if GetSystemMetrics(SM_NETWORK) and $01 = $01 then 
    ShowMessage('Computer is attached to a network!') 
  else 
    ShowMessage('Computer is not attached to a network!'); 
end; 

Взято из https://forum.sources.ru