No-IP Dynamic Update Client (DUC) v3.x uses cleartext credentials that may occur on a command line or in a file. NOTE: the vendor's position is that cleartext in /etc/default/noip-duc is recommended and is the intentional behavior.
https://www.noip.com/support/knowledgebase/running-linux-duc-v3-0-startup-2
https://www.noip.com/support/knowledgebase/install-linux-3-x-dynamic-update-client-duc