You can prevent a user, multiple users, or all user in a group including the All Users group, by doing the following:
1. Logon as an administrator via the Tableau Server web user interface
2. On the left side of the page under Administration click Projects
3. Highlight the project you do not want seen by the users and click Permissions
4. In the next screen click on Add / Edit Permissions
5. On the left side of the subsequent dialogue box select the user, users, or group(s) you want to alter access for
6. On the right side of this dialogue box, select the Deny radio button next to the ability you want to alter, in this case "View"
7. Click submit, then click Assign Permissions To Contents
8. You can now logout of the administrative session and login as any user for whom you denied permissions to view this project
9. Once logged in as the user with denied permissions, click on the Projects link on the left side. This user should not see the project to which their view permissions were denied.
Hope this helps!
Perfect thanks Tracy. I was going down the route of setting up individual sites... This is much neater.