In Alfresco 3.3 the Site Service supported the creation of Public, Private and Moderated Share Sites. These levels of site visibility remain in Alfresco 3.4 with no change to default behaviour.
In 3.3 and by default in 3.4, public sites are visible to everyone. In other words, all authenticated users performing a search for a public site will find it. Of course it is possible to change this as an admin user by simply changing the permissions on any created site objects (which are in Company Home/Sites) but that could be laborious for many sites.
From 3.4 it is also possible to reconfigure Alfresco so that all public sites will be created with a group other than the 'everyone' group having SiteConsumer access. By doing so, it will no longer be necessary to update the site permissions after creation - they will be created with your required permissions.
This has no effect on the other permissions normally applied to sites, namely SiteContributors, SiteManagers etc.
Essentially, you can change public from meaning the 'everyone' authority, which is the default behaviour, to instead meaning 'all the members of a specified group'.
This is done by changing the value of the site.public.group property. You can override the default value for this property by adding the following line to your alfresco-global.properties and restarting the server.
Enterprise users can simply update this property in their JMX client and do not need to restart.
It should be noted that changes to this property only affect the subsequent creation of sites. Any sites that were created before the property update would retain their original permissions.