Wow. I just saw this thread and I think it's a good question, worthy of a good answer. Now, do I have a good answer? I don't know.
Evil, I would say, is anything bad done simply because it can be done. For example, if I were to murder someone, not out of anger, but because I can. I would consider myself evil. Also, anything occultic is evil. That's my point of view, anyway.
Where did evil come from? Though I cant be certain that he even exist, but the obvious answer for me is Satan/the Devil. According to Christianity and the bible, Satan was thrown out of heaven and into hell because he wanted to be God. He then taunted Adam and Eve into eating of the forbidden fruit, and did numerous (and still continues to) other evil deed during the bible.
I don't know if the Christians are right about the story of creation and all, but I'd say if he exist, evil does come from Satan and demons.