By default, all users can access the Username
Lookup page to search for users. As an administrator, you can remove the
user's access to this page if this feature is not required.
Select Manage Roles.
By default, this option is on the Administration home page.
Select a role in the Role Manager page and click
Select.
On the Role Maintenance page, click
General.
Select the Allow Username Lookup access check box from
the Pages section.