CONYERS, Ga. — Last November, election officials in a small Rhode Island town were immediately suspicious when results showed 99 percent of voters had turned down a noncontroversial measure about septic systems.It turned out an oval on the electronic ballot was misaligned ever so slightly and had thrown off the tally. The measure actually had passed by a comfortable margin.The scary part: The outcome might never have raised suspicion had the results not been so lopsided.Amid evidence that Russian hackers may have tried to meddle with last year's presidential election, the incident illustrates a central concern among voting experts — the huge security challenge posed by the nation's 10,000 voting jurisdictions.While the decentralized nature of U.S. elections is a buffer against large-scale interstate manipulation on a level that could sway a presidential race, it also presents a multitude of opportunities for someone bent on mischief.With a major election year on the horizon, the Homeland Security Department has been working with states and counties to shore up their election systems against tampering.States vary widely in what they are doing to tighten security. Colorado and Rhode Island have adopted more rigorous statistical methods for double-checking the votes, while others are making or weighing changes to their voting technology."Always, there's been a hypothetical.