Javascript _Botón derecho ratón deshabilitado

var msg_func_disabled= "Function disabled";

function _IE() {
if (document.all) {alert(msg_func_disabled);return false;}
}
function _NS(e) {
if (document.layers||(document.getElementById&&!document.all)) {
if (e.which==2||e.which==3) {alert(msg_func_disabled);return false;}
}
}

if (document.layers) {
document.captureEvents(Event.MOUSEDOWN);
document.onmousedown=_NS;
}
else {
document.onmouseup=_NS;
document.oncontextmenu=_IE;
}

document.oncontextmenu=new Function("return false")