Apparently, "Zoom bombing" is now a thing, as I just received an email from work about how to prevent it. (It happened to one of our instructors.) If you are not careful with the settings, someone other than the instructor can take over the meeting and broadcast whatever they want. In the case at work, someone took over the online lecture (my guess is a student may have done it, but I don't know) and filled the screen with hate symbols and pornography. It's being investigated as a hate crime.