LOL! You don't have to be a genius to be evil and, speaking from long, hard and repeated experience, you don't have to be a genius to a great deal of harm - just being evil is plenty sufficient. This is especially true when the person who has ill intentions also has disproportionately greater knowledge than you do, or than you can easily get access to in the required time frame. The classic example has been the used car salesman. But better examples are probably the kinds of situations we all encounter from time to time when we get taken advantage of.
I don't know much about computers, so I necessarily rely on others. In an ideal world, I could take all the time necessary to make sure that the guy who is selling me hardware or software that I urgently need is giving me good advice and giving me the product that he says he is. But we don't live in an ideal world. Many people have this kind of problem with medical treatment choices, and for the same reasons. Another, related kind of situation, is where the elapsed time between the time you contract for a service and the time you get it is very long. Insurance and pension funds are examples. Lots of mischief there, and thus lots of regulation. It doesn't take evil geniuses in such situations to cause a lot of loss and harm.
And finally, while this may seem incredible, in my experience those few people who are both geniuses and evil, usually tell you exactly what they are about. They may not say, "I intend to torture and kill you," but they very often will tell you with relish how they've tortured others, or about how they are willing to to torture and kill others. The problem for me for way too long was not taking such people seriously. Turns out, they usually are serious; deadly serious.
The people who cause the most damage do it because they have disproportionate power rather than disproportionate knowledge.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: