What is the best way to combat a "smear campaign" against you?

What I'm talking about is malicious gossip concerning supposed past events and a deliberately one-sided & biased slant on them, mixed with outright false accusations & fabrications, innuendo, in total an orchestrated campaign of deliberate character ination. Talk specifically designed to make others you come in contact with intensely dislike you, and want to disociate themselves from you, even though they really haven't had a chance to actually get to know you yet. The people doing this are doing a good job of remaining "hidden", so direct personal confrontation is not a possibility. If a person is the object of this sort of thing, what sorts of real steps can be taken to combat and mitigate it?