Thanks for the interesting suggestion. I would have no problem with not seeing thumbnails and not being able to search. However, WDCrack sounds like something that would invalidate my warranty and I would prefer to avoid that if possible.
The knowledge base article https://support.wdc.com/knowledgebase/answer.aspx?ID=11807 says “The “backup shares” are not indexed by the My Cloud or the Twonky DLNA Server increasing backup performance.” This is in the context of making a remote backup to a My Cloud, but perhaps the same principle (not indexing backup shares) applies to backups made from a PC to a My Cloud. If so, that sounds hopeful!
If I buy a My Cloud (with firmware version 02.xx…) will I find that it has a “backup” share that I can freely access and to which I can copy files using Windows Explorer and programs like FreeFileSync, and will those files not be subject to indexing and thumbnail creation?