If you would prefer to keep people that you don't know from joining your project team, you can change your project page to "private".
Log in to ChangeX and go to your page.
Click on "Page Settings" to get to your admin area where you can edit all the central information of your page.
Scroll down to "Visibility" and click on the checkbox that corresponds to your choice.
Then click on "Save All Changes" to save your new settings.