Should an instructor tell his/her students before the exam that there are multiple versions of the exam?

Why would knowing in advance matter to anyone except cheaters? This information will not help honest students prepare for the exam or change how they approach it, so for them announcing it afterwards seems just as good as in advance. One argument for announcing it in advance is that some potential cheaters might decide not to try to cheat (and spend more time studying or become a little more honest), but the counterargument is that it might just encourage them to find more effective methods of cheating. I don't consider either of these arguments especially compelling, and I'm not convinced it really matters much whether the announcement is before or after the exam. This issue tends to come up in large courses, which are often pretty standardized. I'd bet the students who care whether there are multiple versions of the exam can easily find out what this professor has done in other large classes, so there usually won't be much of an element of surprise.

I think the answer is "Yes". This causes that low number of students considering cheating on the exam to forget it and put their time towards studying for the exam.

And for other students it would make no difference whether there is only 1 or multiple versions of questions as long as the difficulty of the versions is fairly kept the same.

Update: Following comment of the author about keeping the same level of difficulty among different versions, I still believe that the students have the right to know that there are multiple versions of questions and as an added option you can even tell them that the only difference is on the order of question. That does not make any problem in my opinion.