I found a remarkably good, plain-English description of the insider threats of digital voting systems, and with an intriguing title: Computer Experts Warn of Sophisticated Dagdag Bawas with Automated Polls.
There's little I would add -- just read it! But I will say in advance of a Detailed Reader's comment that, yes, the article is from the Philippines, where there may be an increased sensitivity to insider threats and electoral fraud that there is some parts of the U.S. And yes, the article doesn't provide a comprehensive comparison to similar threats of other voting systems, such as paper-ballot-machine-count or paper-ballot-hand-count or hybrids. For a VERY detailed comparison of risks, we'll have to wait until the EAC's Voting System Risk Assessment project is done. But in the meantime, if you haven't given much thought to how e-voting systems can automate election fraud, point your browser to Bulatlat and have a quick read.