With this hack installed you no longer have the ugly 's=&' in forum url's when the sessionhash is needed. This is made to clone the way vb 3 handles the sessionhash.
Basicly, by default when a user is not using cookies on your forum they see something like this:
Otherwise, the Sessionhash will always be displayed. Erwin is right, though. This does not take into account $sessionhash[sessionid] - which is fairly prominent. Do you know where this variable is being defined?