Can It Be That Bad?
Pulling off a successful vote-fraud attack on electronic voting machines requires considerable skill, which means it won't happen immediately. In fact, I'd be surprised if any of these attacks occur in the next two election cycles, if only because reverse engineering requires both time and testing on a reasonably stable inventory of machines. We haven't deployed enough machines for long enough to make an attack practical.
However, even an "unsuccessful" attack will be devastating if it's widespread enough. An attack that simply crashes a district's voting machines could invalidate an entire local election. Consider the history of PC viruses. The earliest ones displayed amusing (at least, to the creator) messages; subsequent ones either crashed the PC or deleted files; and nowadays, viruses tend to install silent keyloggers or enlist the PC into a botnet. Because the results have economic value, programmers working for money, rather than artistic effect, produce the most recent viruses.
We won't see many amateur voting-machine attacks, except on the local level for relatively small elections. We will see national-scale attacks produced by teams with national-level resources, simply because the stakes are so high and the result is so attractive. Whether those teams work abroad or within our borders remains to be seen.
In reality, we probably won't see those attacks unless we're very, very lucky. We might, possibly, detect an attack after the fact, but the current security surrounding electronic voting machines makes even that fairly unlikely.
Remember: They're smarter, have better resources, and display more motivation than anyone you can hire.
