I have read that people on the ground could pick up the Apollo broadcasts and could also track the craft. If they had had some cursory understanding of NASA equipment, I assume they could have spoofed communications to the Apollo crafts, enabling the most high-profile trolling or pranking events in history. Did NASA take any precautions to prevent this? Were they worried at all about this or just assume no one would do this? I presume that if the Apollo missions happened today, given the high visibility of the event and the potential for interference and notoriety that could give someone, that NASA would have to have taken some measures to prevent Joe Schmo from interrupting the live broadcasts or even from trying to communicate with the astronauts. Was this a consideration at all?
After the Apollo program NASA was kind enough to publish a report about the tracking network that they used.
To make a long story short, communicating with a spacecraft at the moon was a significant challenge even for an organization with the resources and know-how of NASA. The risk of some random person establishing a communications link with an Apollo spacecraft was remote enough to be a non-issue.