Users with the Administrator role can set the Hide Attachment Folders preference at Setup > Company > General Preferences to prevent access to the following folders:
When this preference is set, employees and partners still have access to files that are attached to customer and other record types even if the files reside in one of the folders listed earlier. However, they are unable to view or search for those files in the File Cabinet.
To ensure that only users with adequate permission can access confidential records and associated files in the File Cabinet, the attachments folder is hidden by default. The Hide Attachments Folder box on the General Preferences page defaults to checked for all new customers.
The Hide Attachment Folders preference overrides any restriction applied to a subfolder of the Attachments Received and the Attachments Sent folder.