My students are planning on taking an exam together via Zoom I am a college instructor at a university in the United States. I am giving an exam to my students in a few days, and I am aware that some of them are having conversations about making a Zoom meeting to take the exam together. I take cheating seriously, trying to both dissuade and catch. Nevertheless, if I end up having access to this Zoom meeting, I am not quite sure about what I should do. The exam can be submitted any time during a 24h period, and it is not proctored. I am aware that those conditions could be different, but they are not going to change for this exam.

If I decide not to do anything, I am giving unfair advantage to students not following the academic integrity policy at the school. There is a chance I could present a strong case for the cheating if they are not careful and their answers look identical, but that's not guaranteed.

If I decided to join the meeting using my real Zoom/email address, my guess is that they would get scared right away and leave. If I want to get any information in this scenario, I would have to capture my screen to see who was connected to that meeting. Even if they are using their real names, I would just have a list of the students who were on the call at that moment, and would have zero evidence of what they were talking about.

If I wanted to avoid that, I would have to use a fake Zoom account, which already feels like not the right thing to do. That might give me the chance to stay on the call, and see evidence that it is being used for cheating. But this evidence would just be for me unless I capture my screen/audio, which seems like another thing that might not be right to do.


I am sending them a letter offering my views on academic integrity, in the dissuasion front, but I don't think that would dissuade the proponents of this Zoom call.
What do you think would be the best course of action?
I've spent some time thinking about the problem.
Disclaimer: I believe exams are a way to push students to learn something from the course, grades being an incentive. The solution below may be very unorthodox, so brace yourselves. It's also based on my experiences at an European university, where an instructor has a lot of power in defining an exam and grading it.
I see two ways the Zoom meeting can work:

They solve exams individually, then meet-up for a review session, correct the exams and send them. Which is a good strategy. They will mostly work on the exams alone and during the review session they will gain additional knowledge.
They meet up just after the exams are given and spend time solving them together. It's a bad strategy. Brain storm sessions are usually ineffective, some of the students won't be pulling their weight and, I guess, in the end they will have to spend more time on the exam to turn in the same quality answers as working alone.

That being said, recognising your own weaknesses and turning to someone for help is also a very important skill in life, so I wouldn't mitigate it. I also like very much Buffy's idea to make them cite the sources.
So this is what I'd do:

I'd ask them to cite the sources. When working individually, the sources should differ. If they work together it will be a lot of trouble to not only change the answers, but also the sources.
I'd allow them, however, to work together and ask them to send a contribution report. I'd expect that it would encourage them to divide the workload more equally.
I'd set a different grading standard for individual vs. collaboration work. E.g. the points you lose on a mistake is weighted by a number of people that work on the exam.
I'd allow them to mark one reviewer (whose help doesn't affect a score) and their contribution. I'd encourage the reviewers to also report on their reviews. If the contribution was helpful, it would improve the score of the reviewer. If possible I'd also make myself available as an reviewer.

I believe these solution would change possible ways to cheat into available strategies, making the exam also an interesting experience of collaborative work.