themolecularman is specifically asking for their grounds, I think the "copyright violation" claim is just in order to start the suit, not that they actually violated Apple's copyright in any way.
2. iOS is only licensed for use on bare-metal Apple hardware
3. Therefore, virtualisation is copyright infringement
4. Corellium makes iPhone virtualisation software
Of course, many hacker types would argue if you've got a license to something there's nothing morally wrong with format-shifting it to your heart's content, regardless of what the license or the letter of the law may say. Apple is probably relying on the courts taking a less enlightened view.
i would think that research, including security one, is a fair use with the virtualization being just a research device/tool in this case. Something akin to making an otherwise illegal copy to a different, more lab hardware specific format. Like say you have a copyrighted picture and you make some blow-up or X-ray photo of it for the research.
Very similar in how running macOS on a Hackintosh is a copyright violation. You are only granted a license to the OS to run on Apple hardware. Running their OS in a virtualized environment not on Apple hardware is the same thing.
themolecularman is specifically asking for their grounds, I think the "copyright violation" claim is just in order to start the suit, not that they actually violated Apple's copyright in any way.