This feature was added a long time ago but was never posted.
To add all attachments rights go to Administration > Options > Admin > Add Attachment Types to User Rights.
How it works:
After adding the user rights all non admin users will not be able to change or open the attachment. However they will still see the attachment in the list.
The user rights gives 2 options to each attachment type, view and edit.
The user rights can only be given on attachment notes and not on a category.
Any time a new attachment type is added to the list you must re-run "Add Attachment Types to User Rights". Current users not will lose existing rights it will just add new ones