Students' illicit access to answers for online homework systems
I talked to a group of students about this, with the understanding that of course they would have no personal knowledge of it, but ... er... they might know someone who had experience with Chegg.

Before I had even finished explaining the question, some of them were already laughing. They say that 100% of MasteringPhysics questions are on Chegg, including both the conceptual questions and the quantitative ones.