[Zope] how to count authenticated and anonymous users currently online ?

[Luca Dall'Olio]

I would like to know how many anonymous users are online and also if 
some authenticated users are.
I tried with "guest counter" but couldn't make it work, and tried also 
to inspect temp-folder/session_data but I get a security error.

Is there a way to accomplish this?

Thank you everybody in advance for any hint!

Luca