It may not be surprising to many, but it is certainly entertaining, and one
wonders how the professors can let this happen. Of course in large lecture
courses there is little student-professor contact. But every large course I
have taken has had tests rather than papers. I have no idea how many ghost
test takers there were. But it seems that this happens even when the
professor probably has contact with the student in question.
I have caught cheaters, but usually I make the tests difficult enough that
those who copy are more likely to copy wrong answers. Actually I have
caught cheaters on projects.