There was the issue in Estonia. In Switzerland previously, Internet voting was deployed in three cantons: Geneva, Zurich, and Neuchâtel. The Zurich system has been cancelled for now because of a security audit. Nothing went wrong with the system, but they were doing a security audit and it didn't meet the highest requirement. Zurich now has to decide what kind of new system they're going to proceed with.
There's no really bad breach of an election that I'm aware of. There was, in the United States, a primary or some sort of party vote and there was a breach—a Michigan computer science team did breach that—but in a binding government election, there's been none that I'm aware of.