I've never necessarily heard God described as omnibenovolent, but omniscient. In any case, The existance of evil, while contradictory at first glance, is not a problem at all. If you assume as the Bible notes that God gave us free will, there must be some control in which to decide if a decision is positive or negative. Without that control-case ('evil', as it were), there is no 'good', since these are subjective modifiers. A free-willed person cannot exist where there is only good, nor could one exist where there is only evil, because by logical definition these cases cannot exist. Further, how can you easily show that evil exists? It can easily be argued that even all 'evil' acts have their uttermost good in the long view, because those events may have prevented or caused a domino effect that leads to a greater good.