Quote Originally Posted by Antonio1986 View Post
So in questions is more appropriate also to use: anyoner rather than someone.
Yes, because it's assumed that your question is generic. You're asking someone if they've ever been blackmailed (by anyone). If you wanted to ask that someone if they've been blackmailed by a particular person, yet still remain ambiguous, you'd say "Has someone blackmailed you?" implying you know that it has happened and that it was one specific person or in reference to a particular event. Essentially, there are more known facts implied by saying "someone" over "anyone."