For an extra layer of security, you can add a password to your publication. Anyone attempting to access your publication will have to enter a password to view it.
This feature is available in the Silver plan and higher and can be found in the publication settings menu which can easily be accessed by clicking on the title of the publication in the publication overview.
Don't forget to click Save & Update Publication at the bottom of the Publication settings tab after you selected the option to secure the publication and entered the password.
TIP: When you embed a password protected publication, make sure the website your embedding it on uses a secure https-connection.