I am a professor and get students uploading the wrong file constantly. No porn though, but an assignment for another class you name it. I get how this happens and it is easy to do. I just notify them they uploaded the wrong file and give them a day to get the right one up. I know it is not intentional (if it was, they would not have the assignment at hand to upload, but they always did). If porn got uploaded I would probably just do the same thing, just tell them they have the wrong file etc. If they were constantly uploading porn "by mistake" that would be different.