From the initial hearing in Pennsylvania today, below is about a 90 minute video but I'd recommend starting from 1:02:54.  Where he's giving testimony of some of the (almost rampant) weaknesses of (many) possible voting systems.  Better yet, watch the entire video.

SIDENOTE: To be COMPLETELY honest, I'm practically surprised a modern electronic voting system would use a removable USB drive and, if that's the case, they're likely also using a conventional operating system and drivers like a regular cell phone or computer and simply trusting that 'the internet' is secure.  Sad to say, but I don't even really trust most cryptocurrencies because of the almost glaringly obvious weakness that the operating system itself could "say" practically anything.  (Sorry folks, including myself, that's simply a 'reality check').  A potentially sad possibility is that a crypto isn't ever more secure than someone can personally verify it to be and similarly that applies to the validity of a democracy.  So how to resolve that?  (Triple bonus brownie points that might be able to buy 2 cups of coffee for anyone who can answer that ... and a potential additional issue is to what extent I accept/believe the answer.  Yeah, it sucks)

I'm not claiming that there couldn't be much more secure systems and maybe some of those have been used in this 2020 election, but I've personally worked with electronics, embedded systems, gotten many awards in mathematics, software development and almost received an award in U.S. government as well.  I even recently quit my job because of what appeared to be an overconfidence in the trustworthiness of "the internet" and various interfaces and protocols for distributed communication and can entirely relate with what that man is saying.