From Brian Barrett writing at Wired:

Most people remember the vote-counting debacle of the 2000 election, the dangling chads that resulted in the Supreme Court breaking a Bush-Gore deadlock. What people may not remember is the resulting Help America Vote Act (HAVA), passed in 2002, which among other objectives worked to phase out the use of the punchcard voting systems that had caused millions of ballots to be tossed.

In many cases, those dated machines were replaced with electronic voting systems. The intentions were pure. The consequences were a technological train wreck.

“People weren’t thinking about voting system security or all the additional challenges that come with electronic voting systems,” says the Brennan Center’s Lawrence Norden. “Moving to electronic voting systems solved a lot of problems, but created a lot of new ones.”

The list of those problems is what you’d expect from any computer or, more specifically, any computer that’s a decade or older. Most of these machines are running Windows XP, for which Microsoft hasn’t released a security patch since April 2014. Though there’s no evidence of direct voting machine interference to date, researchers have demonstrated that many of them are susceptible to malware or, equally if not more alarming, a well-timed denial of service attack.