The trick is to make it difficult enough that it is not worth the effort or risk.
Pure electronic machines make it too easy to cheat. Paper ballots (which can be electronically scanned) require a physical object to be manipulated. Thus leaving fingerprints and other physical evidence.
The gross election fraud we have had in the past depends on manipulating objects, which is why there is so much resistance to a medium that is difficult to hack.
Electronic voting is being attacked based on distrust and fear that wizards change the vote, and us peasants can’t tell.
The biggest problem is that, every time you read the file, the total remains the same with electronics.
With paper, you get a different count every time until the correct result is obtained.
You’re exactly right, fireforeffect. The electronics make cheating quick, easy, centralized, widespread, and undetectable.
“many experts say that a paper trail alone can’t solve the problem”
http://www.technologyreview.com/Infotech/20122/?a=f