Everything that is *public* is visible to everyone.  Note that if you are logged in as an admin then you can see everything regardless of privacy.  What the admin sees is not what everyone else sees.

a solution would be to create a plugin (one probably already exsists) that removes the "all" tab from the filter, so your users would only have the "friends, mine" options

there's 1 or 2 plugins that have (or attempted) to handle this.

Thank you all very much. I will look for plugins. I guess my real question comes from Matt Beckett's response: how do I stop categories of items from being public (or from being accessed by unauthoriesed users) at a global level? There seems to be no granularity of access (at the menu level, for example) - as in many other systems - which makes me think that I am missing something.

And yes, I know that that the admin sees everything - the problem is with ordinary users.

Thanks again

Andrew

define 'users at a global level'

also read around here on roles, perms..
even from 3 years back! relevant stuff.
elgg lacks full complement of control hooks for CRUD
and lacks at all granular levels
e.g get entity has hooks R
actions has hooks CUD
but get entity lists does not have easy hooks R* extended
leads to a true ACF variant difficult.

@Andrew... don't let that shite put you off, DDS can be quite accomodating sometimes. ;)

It isn't as easy to find plugins as it used to be, the Plugin section used to have its own search box, so I'll point you and any subsequent members in the right direction...

http://community.elgg.org/plugins/811355/1.8.0/private-river-18

Please post back with the outcome of your search and any testing, to help future members.