The key difference between the new feature and its typical chats is that users must specifically accept invitations to private conversations.
These private conversations can be used with audio calls and text chat, but can only be used on a single device at a time. To that end, Skype is rolling out end-to-end encryption within Private Conversations using Signal Protocol. The content of these conversations will be hidden in the chat list as well as in notifications to keep the information you share private.
Whether Microsoft's latest move to Signal will really help is in question, given the software goliath's past tactics ad cooperation with Uncle Sam.
If Microsoft gives the go-ahead and E2E support lands in the Skype stable release, all of today's major IM platforms will be supporting encrypted conversations as optional, non-default features.
Skype does already offer some degree of encryption that protects the communication channel itself.
Select the contact you'd like to start the Private Conversation with. Private Conversations can only be between you and one other contact.
Signal is an open source project now found in WhatsApp, Facebook Messenger and Google Allo.
Microsoft also clarified that you can't edit a message or forward files within a Private Conversation.
To delete a Private Conversation, simply right click or tap the chat and select Delete. It only works with one-to-one chats at this stage - so video calls and group chats remain unencrypted.
One of the best features of WhatsApp has been its end-to-end encryption since day one. You'll see a "lock" icon next to the conversation.
Private Conversations are specific to a device.
Alas, the UWP version of Skype, distributed on the Microsoft Store, is left out for now. Having to do this every time on Skype would be more of headache than feature.