I got two messages, one of cultmember and one 'nigerian spam' in my private messagebox but also in my regular mail. My mailadres is hidden. How is this possible ?

If your e-mail address is hidden, what you describe is not possible. I would assume either coincidence (same or similar spam sent separately by mail and as PM without any connection between the two) or that you received mail notifications of the PM spam, but not the spam itself. Or perhaps, if the spam was sent as a "reply via PM" to an existing posting and you had checked "send replies to this thread to me via email" on that thread, you could receive identical spam both ways.

Z