Private/Hidden Fields are fields or data points that you can have for your panel member profile that the member can not see or update. The field is accessible to update / edit / sample on only for the admin. This is when you don't want the member to know the field is he/she is being included / excluded in the sample on.
Communities >> Profile >> Global Community Member Profile
Click on Add New Profile Field. Turn on the option for Private/Hidden Field.
Yes, Private/Hidden Fields are included in the import. As the admin, you have access to the data for those fields. The admin can also sample members.
The feature is very useful when you have some kind of private information of the panelist that you don't want them to update easily without any authentic means (i.e. Social Security Number, Voter ID, Driver's License information etc.).
This feature is available with the following license :