Prohibit web page cut screen switching tabs

Prevent being Print Screen 

<script language="javascript"> 
<!-- 
//www.fhadmin.org
function testclip(){ 
try { 
   if(clipboardData.getData("Text")||clipboardData.getData("HTML")||clipboardData.getData("URL")) 
    { 
    null; 
    } 
   } 
catch(e){ 
   clipboardData.setData("Text","") 
   } 
setTimeout("testclip()",500) 
} 
testclip(); 
//--> 
</script>

The above codes are all added in front of </head>