When a new site is created, a corresponding profile is also created to manage the privileges of the guest user. The guest user is a special type of Salesforce.com license that represents the anonymous user of your site.
The guest profile for each site is configured using the native user interface. To view the profile, navigate to the Site Details page for the site and click the Public Access Settings button. Configure the privileges of the guest profile with extreme caution because mistakes can expose sensitive data in your Force.com organization to the entire world.
The guest profile does not appear with other profiles in the Administration Setup area (Manage Users, Profiles). You must use the Public Access Settings ...