[Zope] How to disable anonymous sessions

I thought this must be in the FAQ or something, but 20 min googling does not turn up much usefull. Closest I got was this: http://svn.nuxeo.org/trac/pub/ticket/600 At the moment we have 657 objects in /temp_folder/session_data and this must be quite a bit of overhead. We also have over a thousand "INFO(0) ZODB conflict error" a day, that I suspect are related to this. This should be simple, but I can not spot it :-( Anyone? Gaute Amundsen