browserName = navigator.appName;
browserVer = parseInt(navigator.appVersion);

ns3up = (browserName == "Netscape" && browserVer >= 3);
ie4up = (browserName.indexOf("Microsoft") >= 0 && browserVer >= 4);

//prompt("message on dialogbox","Message in textarea")

mymessage="Desculpe, este comando está bloqueado"

function disableRightClick(btnClick)
  {
    if (navigator.appName == "Internet Explorer" && btnClick.which == 3)  
    {   
      alert(mymessage);
      return false;
    }
    else if (navigator.appName =="Microsoft Internet Explorer" && event.button == 2)    {
      alert(mymessage);
      return false;
    }
    else if (navigator.appName =="Netscape" &&  btnClick.which == 3)    {
      alert(mymessage);
      return false;
    }
    else if (navigator.appName =="Netscape" && event.button == 2)
    {
      alert(mymessage);
      return false;
    }
  }
document.onmousedown = disableRightClick;