Last June I told you about several tested and some theoretical hacks against the Diebold Opti-Scan election system. On Tuesday, Leon County, Fla., again demonstrated these hacks, and will never use Diebold equipment again, according to the elections supervisor.

The county conducted a simple test election, with eight ballots cast on a mock question: Can Diebold election machines be hacked? Six “no” ballots and two “yes” ballots were cast. According to the central tabulator, at the end of the election, the vote count was 7 yes and 1 no.

This particular demonstration involves pre-loading votes onto a memory card used by the election equipment. In the hack, a positive number of votes is loaded for the desired outcome, and a negative number for the other outcome. Then the memory card is used in an election. The tampering is completely undetectable except via hand count of the ballots.

And the hack can be carried out by virtually anybody with a moment’s access to the cards, which according to multiple reports were left lying out in the open for anyone to pick up in many jurisdictions.

Black Box Voting has a more complete description of Tuesday’s demonstration, for those who are horrified at the prospect of voter fraud. And more technical information is available, as well, for those who want to influence future elections.

This is probably why Diebold stock went up when its CEO, Walden W. O’Dell, resigned abruptly on Monday. Stockholders had filed a class action lawsuit against the company, alleging securities fraud as well as covering up problems with its voting machines.

(Hat tip to Bruce Schneier.)