And just in time for the next elections....

[Glaucus]

Diebold voting machines vulnerable to remote tampering via man-in-the-middle attack

Researchers at the Department of Energy's Argonne National Laboratory have demonstrated an electronic "man in the middle" attack that allows remote tampering with the Diebold AccuVote voting system.

 

[FluffyMcDeath]

These sort of attacks are interesting but not my major concern.
The major place where mass tampering can occur without detection is in the code that is installed on the machines that no-one is allowed to inspect. There is no physical record of the votes cast to check the accuracy of the machine.