Select which security groups can see this field. If no groups are selected, all users can see the data in this field.
The Security Groups property only applies to fields used in a Column List layout. It does not apply in a Freeform layout. Furthermore, this setting only controls whether a particular column in the List layout should be shown -- it does not affect data sent from the server to the browser. (So, for example, if you have set a security setting on (say) the 'salary' column, the 'salary' column will be hidden in the List, but the List data that is sent from the server to the browser will still include the salary data).
If you want to apply security group restrictions to one or more fields in a List with a freeform layout, you must apply these settings to the SQL Query on the Data Source tab. The advantage of doing this is that the security groups will be applied at the query level (this restricts access to the data by excluding it from the SQL Query, meaning it is never downloaded to the user's device).
If the List is based on a SQL query, uses a freeform layout, and you have defined security groups for any field in the List data source, Alpha Anywhere will ask if you want to copy your security groups settings to the Data Source tab when the List Builder is closed.