One key bit from the Senate hearing on Russian Interference in U.S. Elections
Senator Richard Burr:
When you and your colleagues hacked election systems, did the administrators see your intrusion into their systems?
"The one instance when I was invited to hack a real voting system while people were watching was in Washington, DC, in 2010. In that instance, it took less than 48 hours for us to change all the votes and we were not caught."
— Computer Security Researcher,  J. Alex Halderman