When you create or edit a project you have the option to decide it's privacy. There are 3 options to choose from:
Account - Visible to all creators & invited collaborators - Projects with this privacy setting will be visible to all creators (in the ALL filter setting on project views) and any collaborators that you specifically invite to the project.
Project - Only visible to people who are invited to the project - Projects with this privacy setting willonly show to people if they have been specifically invited to the project and show on the people page of the project.
Private - Only visible to me - Projects with this privacy setting will only be visible to you, in any circumstance.