These machines being unhackable is laughable to every security researcher. Currently, there's no possibility to create unhackable devices. The chances of being hacked increase drastically when the device is connected to the internet. There were (and probably still are), for example, critical flaws in security chips like Google Titan M, which are types of projects led by multinational corporations that have the best of the best security researchers. Titan M for example has a thermal sensor, that tracks temperature transients as a form of possible tampering. All of that is to securely unlock your phone, so you can take a photo of your kid or text a friend... Just imagine how extreme standards SHOULD be enforced on vote-counting machines.