Based on preliminary reports published by the team of experts that New Hampshire engaged to examine an election discrepancy, it appears that a buildup of dust in the read heads of optical-scan voting machines (possibly over several years of use) can cause paper-fold lines in absentee ballots to be interpreted as votes… New Hampshire (and other states) may need to maintain the accuracy of their optical-scan voting machines by paying attention to three issues:
Routine risk-limiting audits to detect inaccuracies if/when they occur.
Clean the dust out of optical-scan read heads regularly; pay attention to the calibration of the optical-scan machines.
Make sure that the machines that automatically fold absentee ballots (before mailing them to voters) don’t put the fold lines over vote-target ovals. (Same for election workers who fold ballots by hand.)
Read more: schneier.com