There exist many variations and spins on this; but the original riddle goes like this:
Is God willing to prevent evil, but not able? Then he is not omnipotent.
Is he able, but not willing? Then he is malevolent.
Is he both able and willing? Then whence cometh evil?
Is he neither able nor willing? Then why call him God?
The weakness obviously lies in the deduction on the second premise. It completely leaves out the possibility that there might be a deeper underlying motive for an able God not want to ban evil without him being considered malevolent.
If we understand and analyze the different types of evil, I can find an alternative explanation rather then resorting to God being malevolent.
1. Evil as result of free will.
Many evil things comes from mankind's free will. The problem is freedom of Choice. If you believe -like I do- that life is a test; then God would defeat his own purpose by preventing evil! Stopping evil would prevent free will.
2. Necessary (relative) Evil.
Of course, not all evil of the world can be traced back to human choices. There is a second type, which I'd like to call relative evils. Because their "evilness" is relative to one's perspective. Death for example, gets a whole new perspective if seen as a transition rather then an end. These are things that serve a purpose. It can be a practical purpose, like the mentioned death in order to transit from one world to the next. But other things as hardship can also have practical benefits. For example, it can teach people. Ever noticed how generally speaking, people who had little or no hardships in their life have a higher tendency to be arrogant? Rightful punishment could be another practical evil. As controversial as some of these might be, the point remains that we can imagine alternative motives, without resorting to judging our creator as malevolent for allowing these "evils".
3. Hardship as a test.
And then finally a third type of evil, in general all sorts of hardships and suffering that do not serve a direct purpose in this life. However even these can gain a new perspective if seen in the context of life being a test. There's a huge difference between a poor man who doesn't steal and a rich man who doesn't steal. From that perspective one could consider being poor as a blessing rather then a curse, as it can increase one's reward in the hereafter.
So is God malevolent or not? Well I certainly don't think I can prove my view is right. But I do hope I've just shown that the problem of evil is inconclusive as there is room for alternatives.
1. Evil as result of free will.Yes many evil acts are the result of human action and can be explained by our freewill. However freewill is a very tricky subject - particularly when you bring an all-powerful, all-knowing God into the equation. The problem is that our choices are determined by factors that such a God must have defined unless he somehow built in to our creation the ability to act in a way he did not calculate when he made us.
2. Necessary (relative) Evil.This is only an assertion. There is no evidence to prove that evil is a means to an end. I certainly hope that the terrible suffering, disease, disaster and death serve a good purpose and will be balanced out in the grand scheme of things - but the fact is that neither you nor I know that that it does and wishing something would be true because we want it to be so - does not make it true.
3. Hardship as a test.Again, this is only an assertion and makes little sense when you examine it. Why does an all-knowing God need to test us? So he can say I told you so? So he can justify torturing them for eternity? And what is he testing? Whether we are willing to have faith in something that is unsupported by any real evidence? (If so Christians, Hindus, Jedi Knights, and devotees of the Mbombo who 'vomited out the world', have also passed the test.)
Is God malevolent? I find it hard to think that if a god does exist he is a malevolent monster. So either he doesn't exist or he really does have a very good reason for all this. However what I am quite sure of is that no God can call himself Just, Merciful or Forgiving if he also tortures his creatures for coming to the conclusion that there is no God or that religions are false.
The fact that the Qur'an spends so much time condemning those who don't believe to the most gruesome and cruel torture, makes it blindingly obvious it is the work of man and not a god - if one exists - regardless of what the answers to the above philosophical questions are.
Topic: The riddle of Epicurus a.k.a. the problem of evil.