If I remember right (but I could be wrong) I thought it was indicated by someone one that remote access (other than FTP) to the My Cloud uses some form of SSL for security. The WD Sync program has the option to enable SSL for local network transfers. Remote access FTP is not secure at all, one could use SFTP for a more secure access but this possibly involves editing one firmware file to enable non admin access via SSH.
There has been some past discussion on some potential security issues with the My Cloud in the following threads. It is possible that those discussions may answer your question about how the remote access security works.
http://wdstagingsplit.staged-by-discourse.com/t/latest-firmware-still-vulnerable/96743
http://wdstagingsplit.staged-by-discourse.com/t/reporting-security-vulnerabilities/96387
http://wdstagingsplit.staged-by-discourse.com/t/how-secure-is-wd-my-cloud/95914
http://wdstagingsplit.staged-by-discourse.com/t/where-to-report-vulnerabilities/95898
