The default visitor counter is not a real visitor counter, cause every time the footer is reloaded (and that's with every change!), 1 is added.
Made a change in counter.php, it checks if the current user in known in whos_online. If so, nothing changes. If not, the counter is added with 1.
For this to work, the following files need to be edited:
counter.php (also in package)
application_top.php
footer.php