In this Oct. 14, 2016 photo, a technician works to prepare voting machines to be used in the upcoming election in Philadelphia. These paperless digital voting machines, used by roughly one in five U.S. voters last month, present one of the most glaring dangers to the security of the rickety, underfunded U.S. election system. Like many electronic voting machines, they are vulnerable to hacking. But other machines typically leave a paper trail that could be manually checked. (AP Photo/Matt Rourke)