A top 10 MBA program my partner went through had several people cheating in the program. I'll give you some anecdotal notes. Some cheaters get discovered and "outed" (esp those the group didn't like) when they brag during parties, some never gave up enough evidence to make an accusation official, others would talk about hiring CPAs for accounting exams/projects. Many in the class were concerned on whether normal study groups counted as cheating, as defined by the honor code!
A sibling program at the university exposed a cheating ring of ~15-20 people, and I think many were surprised that the result was to simply zero their grades for that class instead of more severe action.
/e I mention incidents and sizes since these programs are not thousands of students but tens or hundreds.
