Researchers at Princeton intentionally injected malicious software into a Diebold Accu-vote-TS voting machine for the purposes of security research. In an online video the researchers, Ariel J. Feldman, J. Alex Halderman, and Edward W. Felten, conducted a pretend presidential election in which George Washington receives four votes to Benedict Arnold's one. Yet, when the voting machine is queried at the end of the day, its paper printout states that Arnold received three votes to Washington's two. Even the memory card, designed as a backup, reports the same fraudulent result. There is no way for an observer after the fact to disprove that voters did not give Arnold three votes to Washington's two--except that we saw in the video that the voters did in fact vote differently. The researchers at Princeton exploited well-known software flaws with the Diebold Accu-vote-TS voting to construct their malicious code and cited lax security procedures at the polling sites, such the ability to pick the lock on the memory card, as a means of spreading the malicious code. Full details are available in this PDF report. See also this story on News.com.