I wonder who would launch such an attack and what the motivation would be? Would it be, "because I can" sort of hacking or someone hired or with more purpose. In any event, this is clearly a risk. Take a look at the other stuff going on on the Black Box Voting site. I think it's quite important.
MONDAY Nov 1 2004: New information indicates that hackers may be targeting the central computers counting our votes tomorrow. All county elections officials who use modems to transfer votes from polling places to the central vote-counting server should disconnect the modems now.
There is no down side to removing the modems. Simply drive the vote cartridges from each polling place in to the central vote-counting location by car, instead of transmitting by modem. “Turning off” the modems may not be sufficient. Disconnect the central vote counting server from all modems, INCLUDING PHONE LINES, not just Internet.
In a very large county, this will add at most one hour to the vote-counting time, while offering significant protection from outside intrusion.
It appears that such an attack may already have taken place, in a primary election 6 weeks ago in King County, Washington -- a large jurisdiction with over one million registered voters. Documents, including internal audit logs for the central vote-counting computer, along with modem “trouble slips” consistent with hacker activity, show that the system may have been hacked on Sept. 14, 2004. Three hours is now missing from the vote-counting computer's "audit log," an automatically generated record, similar to the black box in an airplane, which registers certain kinds of events.
via David Weinberger