Salon has a very good review on electronic voting fraud. (Unfortunately you need to be a subscriber to view the entire article.) Snippett:

[Bev] Harris has discovered that Diebold's voting software is so flawed that anyone with access to the system's computer can change the votes without leaving any record. On top of that, she's uncovered internal Diebold memos in which employees seem to suggest that the vulnerabilities are no big deal. The memos appear to be authentic -- Diebold even sent Harris a notice warning her that by posting the documents on the Web, she was infringing upon the company's intellectual property. Diebold did not return several calls for comment. The problems Harris uncovered are not all that surprising; technologists have been warning of the potential for serious flaws in electronic voting systems -- especially touch-screen systems -- for years. In July, scientists at Johns Hopkins and Rice found that security in Diebold's voting software fell "far below even the most minimal security standards applicable in other contexts." The report prompted Maryland Gov. Robert Ehrlich to order a review of the Diebold systems used in his state. Many of the world's most highly regarded computer scientists have called on voting companies to build touch-screen systems that print a paper ballot -- a "paper trail" -- in order to reduce the risk of electronic tampering.