I found a disclaimer script from the web and installed on my site, I am newbie to javascipt, and hope someone could help.

How can I modify the script so that every time a user close the browser windows and visit the site, they need to accept the disclaimer again??

Thanks a lot for your suggestion in advance.

Code:
<script type='text/javascript' >
// Disclaimer DHTML
// Copyright Outils.XXX 2012

function ScanCookie(variable)
{
 cook=document.cookie;
 variable+="=";
 place=cook.indexOf(variable,0);
  if(place<=-1) return("0");
 else
 {
  end=cook.indexOf(";",place)
  if(end<=-1) return(unescape(cook.substring(place+variable.length,cook.length)));
  else return(unescape(cook.substring(place+variable.length,end)));
 }
}

function Entrer()
{
 document.cookie="disclaimerok=oui;path=/;";
 if(document.getElementById) document.getElementById("disclaimer").style.display='none'
 top.location.href=location.href;
}

if(ScanCookie("disclaimerok")==0)
{
 document.write(""
 +"<style type=\"text/css\">"
 +"<!--"
 +"object{ visibility:hidden; }"
 +"#disclaimer{ text-align:left; }"
 +"#disclaimer-fond{ position:absolute; z-index:15000; width:100%; height:2000px; background:#fff; text-align:center; line-height:normal; clear:both; filter:alpha(opacity=95); -moz-opacity:0.95; opacity:0.95; }"
 +"#disclaimer-conteneur{ position:absolute; z-index:15001; width:100%; text-align:center; clear:both; }"
 +"#disclaimer-cadre{ width:718px; padding:10px; margin:150px auto 0 auto; text-align:left; background:#fff; border:#ddd 1px solid; }"
 +"#disclaimer-cadre b{ display:block; padding:10px 0 10px 0; text-align:center; font-size:21px; color:#666666; }"
 +"#disclaimer-cadre font{ display:block; padding:10px 0 20px 0; text-align:center; font-size:21px; color:#666666; }"
 +"#disclaimer-cadre p{ margin:0; padding:10px; font-size:16px; color:#666666; }"
 +"#disclaimer-cadre .boutons{ margin:0; padding:10px; text-align:center; }"
 +"#disclaimer-cadre a{ text-decoration:none; font-size:36px; font-weight:bold; color:#6D28AA; }"
 +"#disclaimer-cadre a:hover{ text-decoration:underline; }"
 +"-->"
 +"<\/style>"
 +"<div id='disclaimer'><div id='disclaimer-fond'></div><div id='disclaimer-conteneur'>"
 +"<div id='disclaimer-cadre'>"
 +"<b>Site Disclaimer</b>"
 +"<p>Message here</p>"
 +"<div class='boutons'><a href='#' onclick='Entrer(); return(false)'>Accept</a> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a rel='nofollow' href='http://www.google.com/'>Leave</a></div>"
 +"</div>"
 +"</div></div>"
 );
}
</script>