Can anyone see my presentation?
By default, all presentations are accessible via yourname.viewbook.com/name_of_your_presentation. You always have to option to share your work and to invite people to see it.
To keep out uninvited guests, people need to know your Viewbook URL and the name of your presentation to be able to see your work.
If you're afraid someone will still be able to see your work without your permission (by guessing the correct url for example) you can disable the 'alias' link by activating the 'private link' in the 'details' tab in the presentation 'options'.
Note: When choosing the 'private link' your presentation will not be indexed by search engines.