Election Day voters in 10 states, or parts of them, will use touch-screen voting machines with rewritable flash memory. If malware is inserted into these machines that’s smart enough to rewrite itself, votes can be erased or assigned to another candidate with little possibility of figuring out the actual vote. Even if a hack is suspected, or proven, it would likely be impossible to do anything about it. Pennsylvania is attracting the most concern because of the lack of a paper ballot and no paper record of an individual’s vote.”]
Source: https://www.csoonline.com/article/3128077/if-the-election-is-hacked-we-may-never-know.html