User closing browser(X) instead of logoff

Hi,

In portal, when a user instead of logging out, closes the session abruptly by clicking on close button, the portal does not close the user session. When the URL opened again in the same terminal by anybody, the  portal opens with the previous user’s open session.

i used below code in masthead, but no luck.

var closing;

window.onload = function() {

     closing=true;

}

window.onunload = function() {

     if(closing) {

          EPCM.raiseEvent("urn:com.sapportals.portal:user", "logoff", "");

     }

}

Portal Version : 7.0

Please help me to resolve.

Regards,

Anand