var rnd = Math.ceil(Math.random() * 4);

if (rnd == 3) {
	window.open('http://popup.localscripts.nl/hollebolle_popups/1/popup.htm' , 'l', 'width=10, height=10, toolbar=no,location=no,status=no,menubar=no,scrollbars=no,resizable=no');
}