With 4.4.0 version of Web Experience Cloud Visitor API, you can apply SHA-256 algorithm to the values passed to setCustomerId() method.
SHA256 Hashing Support for setCustomerIDs
This makes securing customer-identifiers much easier. I have been told that there are plans to add capability to mention SALT which will make it even more secure.
However, equivalent Mobile SDK methods (syncIdentifiers), both for iOS and Android do not have this capability, even in Adobe SDK v5.
Benefit: This will make customer-id syncing process consistent across both Web and Mobile-App channels, which means a customer will be identified using a single secure-id across both channels.