We've just released an updated Unity3D client that removes a dependency on Yahoo's play.yahoo.com site.
If your game uses the Unity3D client library to build iOS games, you need to upgrade and release a new build of your app in the near future. This is in order to avoid your game breaking when Yahoo removes the play.yahoo.com site in the future.
Yahoo had accidentally removed the play.yahoo.com site which caused new installs of iOS games built with the Unity3D to fail after install when they called out to play.yahoo.com. However, Yahoo has since revived the play.yahoo.com site.