how did they get this popup thingy

<SCRIPT LANGUAGE='JavaScript'>
 
var layer=''; layer += '<'+'div id="postit" style="position:absolute;width:555px;height: 465px;z-index:1;left:50px;top: 50px; overflow: hidden; background-color: #fff;border:1px solid #555;border-bottom:2px solid #555;margin:0;padding:0">'; layer += '<'+'div align="right" style="margin:0;padding:5px;background-color:#aaa">'; layer += '<'+'input type="image" onclick="closeit()" src="http://descargas2.tuvideogratis.com/closed.gif" width="16" height="14" border="0">'; layer += '<'+'/div>'; layer += '<'+'div style="padding:0; margin:0">'; layer += '<'+'IFRAME SRC="http://p1.webcamspromociones.com/webm/torrentesx/layer4/index.html" WIDTH="555px" HEIGHT=465px" style="border:0px" BORDER=0><'+'/IFRAME>'; layer += '<'+'/div>'; layer += '<'+'/div>'; layer += '<'+'script'+'>'+'\n'; layer += 'var ns4=document.layers\n'; layer += 'var ie4=document.all\n'; layer += 'var ns6=document.getElementById&&!document.all\n'; layer += 'if (ns4)\n'; layer += 'crossobj=document.layers.postit\n'; layer += 'else\n'; layer += 'if (ie4||ns6)\n'; layer += 'crossobj=ns6? document.getElementById("postit") : document.all.postit\n'; layer += 'function closeit(){\n'; layer += 'if (ie4 || ns6){\n'; layer += 'crossobj.style.display="none";\n'; layer += '}else{\n'; layer += 'if (ns4){\n'; layer += 'crossobj.visibility="hide";\n'; layer += '}\n'; layer += '}\n'; layer += '}\n'; layer += '<'+'/script>\n'; document.write(layer);
 
</SCRIPT>