For almost 17 years, states and counties around the country have conducted elections on machines that have been repeatedly shown to be vulnerable to hacking, errors and breakdowns, and that leave behind no proof that the votes counted actually match the votes that were cast. Now ... states and counties across the country are working to replace these outdated machines with new ones. The purchases replace machines from the turn of the century that raise serious security concerns. But the same companies that made and sold those machines are behind the new generation of technology, and a history of distrust between election security advocates and voting machine vendors has led to a bitter debate over the viability of the new voting equipment. The draw of the new machines, called ballot-marking devices (BMD), is the promise of a paper ballot. But there are concerns with the integrity of the paper trail a BMD would create at every stage. Many BMD models on the market print a sort of two-in-one ballot with one section to be read by machines and another to be read by humans. Barcodes - or QR codes - that represent a voter's choices are printed on the ballot along with plain text showing, presumably, the same information in a way people can understand. When the ballot is scanned, it is the barcode that is scanned and counted, not the text that voters can read. If a barcode is printed that represents a different choice, or the scanners were hacked, voters would not know the difference.