its all about how the window is launched...
popup blockers work by defusing the javascript as javascript is client side
normal popups work with something like :
code:
window.open
mess.be (FASTCLICK.COM to be more percise) combats popup blockers by insted of plain javascript it writes the popup to auto load with the document
code:
<script language="javascript"><!--
var dc=document; var date_ob=new Date();
dc.cookie='h2=o; path=/;';var bust=date_ob.getSeconds();
if(dc.cookie.indexOf('e=llo') <= 0 && dc.cookie.indexOf('2=o') > 0){
dc.write('<scr'+'ipt language="javascript" src="http://media.fastclick.net');
dc.write('/w/pop.cgi?sid=6164&m=2&v=1.8&c='+bust+'"></scr'+'ipt>');
date_ob.setTime(date_ob.getTime()+43200000);
dc.cookie='he=llo; path=/; expires='+ date_ob.toGMTString();} // -->
</script>
oh yeh, it also sets a cookie per day so u dont get it everytime you visit the site
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