Summary: You're supposed to turn in an assignment tomorrow via email. You're behind. So, you go to this website, and for $4, you can buy a file which looks like a completed version of the assignment, but is horribly corrupted. A couple of days later, when the instructor opens the file --- or, rather, tries to, and fails, the instructor contacts the student and asks for a clean copy. Voila: you just bought yourself a few days extra on the assignment.
Of course, there are ways to detect this sort of dishonesty ... timestamps, hidden information in the documents, and so on. Regardless, having to look at this sort of thing makes life even more annoying for instructors.
When did professors become the enemy?