Skype is one of the few popular messaging and communications services that doesn't yet employ full end-to-end encryption. But that's set to change. Skype Private Conversations is coming following the announcement of an agreement between Microsoft and Open Whisper Systems (makers of the Signal app).
Private conversations is a new feature beating rolled out through Microsoft's Insider program. It only works with one-to-one chats at this stage - so video calls and group chats remain unencrypted.
Not all chats will be private with the option only available if you choose the recently added "New Private Conversation" option when you start a new chat.
Skype has been the holdout when it comes to encrypting messages with all the other big players including end-to-end encryption either by default or as an option.
In addition, if you've been using Facebook's sign-in service to log into your Skype account - you'll need to update your credentials as that mode of connection has been shut down.