Bona = good. Mal means opposite. The opposite of good is bad. Why does this say 'evil'? Should not evil be malbonega?
Bad can be used as a noun and should be accepted (although badness or the bad are more common expressions). I have submitted it as an alternate and it will eventually be accepted, I'm sure.
As far as malbonego goes, I have mentioned this elsewhere as a more nuanced way of conveying the additional gravity of English "evil." It is technically correct so you are free to use it. That being said, evil is certainly one of the meanings subsumed under the variety of definitions for malbono, just as English evil is subsumed under the broad meaning of bad, so the current translation is perfectly acceptable.