Earlier quoted context omitted.
I (undegrad. prof. of mathematics, Spain) did "nothing" (see below) except prepare (not so) different exams. Same results as always. Exactly the same. Someone will have cheated. Well, as always: I am sure people cheat at my exams as they do at any other. I do not repent and I do not think I would do otherwise. *However*: I DID spend a lot of time preparing materials, attending tutorials, replying to emails, correctin…
I had an very relaxed Indian professor who served as as department chair when I went to university and he always had open book/note quizzes, tests/exams with no restrictions. These exams weren't designed to be more difficult, some answers you could very quickly reference from the associated text, handouts, or your notes. People asked if he was concerned that people cheated or wouldn't learn anything and he once gave…
That can hurt the school's reputation if it becomes known for passing students who aren't actually prepared to do the work. Employers would prefer to recruit from schools where having a diploma actually means one is capable of doing what the job requires.