Team Foundation Server 2010 : Too many users in your Team Project

By default, you have half of the world accessing your Team Project in Team Foundation Server 2010. Since it is based on the AD group, the amount of people automatically added to your project is particularly impressive in large companies.

This is an old problem, since TFS 2008 ; you have to remove the security group : "Team Foundation Valid Users" which could be found in the "Project Security" form.

http://msmvps.com/blogs/vstsblog/archive/2008/08/06/users-can-see-all-team-projects-after-upgrading-from-tfs-2005-to-2008.aspx