When officials combined information from the three ballot scanners for a grand total, the software glitch added thousands of votes. In reality, only 5,613 ballots were cast, not the 10,488 initially reported.
"It's not that we found ballots. It's not that we lost ballots," Pennington County Auditor Julie Pearson is quoted as saying. "It's just combining them didn't work."
No one suspected a problem, Pearson said, because the scanners had worked smoothly all night.
But late in the evening, election officials started to question the initial vote tally of 10,000 votes, which seemed excessive. A manual audit revealed the error.