A hidden contest is marked with a crossed-out eye icon on the contest listing. In a hidden contest, no one except the contest holder can see the entries submitted in a contest. Designers can only see their own designs and people browsing the site won’t see any of the designs at all.
In hidden contests, as a designer you dont have to worry of getting copied or about protecting your original concepts. You can express freely.
Remember: Once a contest has been made hidden, it will remain hidden for the duration of the contest. As soon as the contest ends, all entries will become visible to everyone using the site.