...
This property determines whether the value saved in the submissions repository is hidden when viewed in the web submissions UI. The value is not currently encrypted in the database. Check Check the checkbox if the data users will enter into this field contains sensitive data that should not be visible when viewed in the web UI. In a future release sensitive Sensitive field values will be encrypted in the submissions database using an SHA algorithm. The control must be designated as a Saved Field in the form. This property does not enable hashig of the value stored in the XML document.
CSS Class
This is the control’s class name that was added to your form's XHTML markup. You can use this CSS class to reference the control in any CSS when customizing themes.
...