This would be a good question to post to the FileMaker Pro forum instead of Report an Issue which is intended for reporting possible bugs found in a FileMaker product.
You can use settings in Manage | Security to control access to specific tables or even records within the table, but not a specific field. You could move this field into its own table with a one to one relationship to the original table. You then can limit access to just this one field as it is now in a separate related record.
Or you might create two copies of the same layout. One layout can be set to prohibit access to all the fields while in browse mode except the one field and the other layout can be set to allow access to all the fields. You'd then use scripts to select the layout copy that's correct for a given user's privilege set or account name. This approach is much less secure than the first, but doesn't require radical surgery on your tables to implement.