Voting for more candidates than open seats. For example, voting for 4 council members where the ballot specifies "Vote for not more than 3."

An overvote may disqualify an entire paper ballot, even if the rest of it is filled out correctly. Electronic [voting machine]s prevent people from casting overvotes, but they are shockingly vulnerable to [voter fraud].
> Hey! Even if you WANT to elect both Clinton and Obama as 2008 Democratic nominees for co-president, the [voting machine] won't let you; it's an overvote.