Please find attached 2 examples of the same calendar entry, 1 public and 1 private. The only difference is the CLASS field, this can be set to PUBLIC, PRIVATE or CONFIDENTIAL (if left blank it should default to PUBLIC)
I have also attached the latest ICS calendar format specification, setting the visibility CLASS is from page 54, in case it is required.
It would be nice if this option was available and set before the Outlook Calendar Sync to stop any accidental sharing of Private information.