How forthcoming should I be with new people I meet about my checkered past?

My past is not a source of pride for me. Over four years ago, I read "Atlas Shrugged." That book radically altered the radical change I was already bringing into my life -- for the better. I've recently begun meeting Objectivists in real life, and I dislike discussing my white-trash, moocher-esque history with these new acquaintances. (At the time, I was between 17 and 20 years old.) I rarely share these details with non-Objectivist friends, but I fear their judgment less. If I shared my past with an Objectivist, I think they might choose to cut ties with me immediately, given that they don't know me well. However, given my past, I have a clearer understanding of the irrational, twisted, cruel, and nasty nature of people who choose to live like leeches off of other human beings. I think that sharing these experiences with others can be a source of strength to them. (I don't want others to stumble into these poor decisions when they could do better!) So how much of my past should I share with other people, and how should I share it?