So I strongly suspect that one of my students is asking all their homework questions here. In particular, all the questions that user8917 has asked about probability are homework questions that I have assigned in my current course. I am using a standard text (Pitman, Probability), so coincidence is possible, but there are many problems in our textbook that I have not assigned -- it seems unlikely that a person studying the book on their own, or even a person in another class using the same book, would choose exactly the same set of problems to be handed in.
My policy on academic dishonesty is simply that students cannot copy their answers from any source, although of course with relatively simple problems this is difficult to impossible to enforce. I of course would not want to forbid my students to use sites such as this one - if they have more general questions, or questions which are not specifically "how do I do this homework problem". But I don't want people solving my students' homework questions for them! I would appreciate the community's advice on what I can do here.
This is in some respect a repeat of this question, regarding a similar anonymous user who consistently asked homework questions; the major difference is that I, the instructor, am the one who noticed this.