Actors and their agents are warning that the use of non-disclosure agreements (NDAs) in casting is a huge and increasing problem, with many major producers overly sensitive about the secrecy of their projects.NDAs are often in the news - and usually for unscrupulous reasons. In recent years, they have been used to silence victims of assault or bullying; disgraced film producer Harvey Weinstein was found to have used them against women he'd attacked.