I have been thinking about this concept and I think I need a more biased opion to help me refine it a little better.
I propose god is the ultimate source of evil and even the most evil thing that exists (assuming a god exists at all that is). I would base this most off of the christian concept of god but I think it applies to any kind of creator god. But I am going to explain it from a christian perspective so if your idea of god isn't a perfect creator god then this probably doesn't apply.
Anyways, satan is considered the ultimate evil right? But for satan to be more evil than god would mean satan would have to be at least that more powerfull than god in that arena. But if god is the creator, than satan cannot be more powerfull than god in any way. How can a creator create something greater than himself especially if the creator is already the ultimate thing? He can't, if god could create something greater than himself, he wouldn't be god anymore, he would be second to the new god which he just created.
So, if nothing can be greater than god, god must be the greatest evil force in the universe. Of course this would mean god would also be the greatest good in the universe which would mean god is really the greatest nuetral force in the universe. That raises a whole miriad of other questions but that is for another discussion. The bottom line, regardless of whether god is directly controling the evil in the universe, god will always be the ultimate source fo that evil, like water spraying from a hose, you can control the water by manipulating the nozzle but the ultimate source of the water is at the spigot, the hose is irrelevant. Just as satan is irrelevant as god is the true cause of evil.