What is "clear session"?

[Admin]

And it does mark all forums read.
If you don't want that, remove this code from the code above:

  if ($bbuserinfo[userid]!=0 and $bbuserinfo[userid]!=-1) {
    $DB_site->query("UPDATE user SET lastactivity='".(time()-$cookietimeout)."',lastvisit='".time()."' WHERE userid='$bbuserinfo[userid]'");
  }