Roles and permissions

Hi, we are using Moodle 2.7.3 and I am also trying to hide the course list from unauthorized viewers. I have set the frontpage to only show news for users that are not logged in and to show news and courses for logged in users. I can hide the Navigation block for guest users, but if I do a google search for one of our teachers, the second result is a link to the moodle course list which shows the list of courses (…). We want to hide this list from the general public accessing it via google search, but I couldn't find the appropriate option. Any help is appreciated. Thanks in advance, Christian