What is the nature of evil?

One of the most interesting topics in philosophy is evil, what is evil? What lead us to do evil? Is it a useful concept or just useful to religion? I think that it is interesting to think about the nature of evil. First we need to define what evil is, and create a good definition of something is never a trivial task. Lets start with the following definition: Evil is an action or actions that direct or indirect hurt one or more living beings.
That definition is to broad, follow it to its conclusion and we will discover that we are all evil, because everybody hurts living beings everyday, because that are microscopic creatures, like bacteria, that we don't see but we kill everyday. Therefore we may need a definition that take into account only sentient beings like crabs, dogs, insects and so on. But now we have to define consciousness too, and that is a really difficult task too.
Lets do the following, lets put aside the task of define what the hell is a sentient being and define as evil all the actions that we do with or without intention, that hurt others sentient beings.
Now that we know what is evil, let think about we lead us to do it, well, we know that there are many causes of evil actions, the non-intentional causes, are just actions with undesirable results, on the other hand, the intentional ones can be cause by a variety of reasons. We can do evil things because we don't have empathy, or because we are angry, or just because we are sadists. who knows? At this point of my essay the reader must be already full aware of the total lack of good philosophy in it. What happen with this text was a combination of a creative block with a strange desire of just write a stream of thought, the result is draft of a text about evil. I will probably return to this topic in the future, probably with a better and more inspired text, just happened that I am to evil not to publish it.