请问如何屏蔽用户按alt+F4关闭IE窗口

<HTML>
<HEAD>
<TITLE>GDELJYH</TITLE>
<META name=VI60_defaultClientScript content=JavaScript>
<META NAME="GENERATOR" Content="Microsoft Visual Studio 6.0"><script>
function Forbid_Key(){
try{
if ((window.event.altKey)&&(window.event.keyCode==115)){ //屏蔽Alt+F4
    window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");
    return false;
}
}catch(e){
alert(e.description);
}
}
document.onkeydown=Forbid_Key;
//-->
</SCRIPT></HEAD>
<BODY></BODY>
</HTML>