How Do You Restrict Access to Custom Fields?

Background: I have successfully created a custom tab along with custom fields for our Employee records.  The purpose of these fields/tab is to capture certain employee-related information which is confidential.  I have set the security such that only certain roles can see the tabs when an employee record is accessed.  So, everything works as expected so far....

Problem: It seems that any user, regardless of role, can select/search/view these fields when creating a custom search.  In other words, even a person who does not have visability to the custom tab (and therefore, the custom fields) can create a custom search to display the fields.  Perhaps I have set up these fields with incorrect security.