We had an instance today of a user posting two questions to MSE during an online exam - the questions were from the exam. The students taking the exam are expressly forbidden from using any internet resources apart from the material on the course website. One of the questions was answered helpfully, and the other was quickly closed, but still had helpful comments.
If we could identify the student (which could probably be done from their IP address) then they would be in serious trouble for cheating.