According to this story, the Nedap ES3B can be privacy compromised by eavesdropping on radio emanations. It is not clear from the story whether the machine must be tampered with first, and the manufacter of course insists their machines will be clean.
Transparency is the Achilles heel of e-voting. Building a machine which faithfully records votes is easy. Building a machine which can be seen to faithfully record votes without compromising the secrecy of the ballot is next to impossible.
Making voting software open source would improve this transparency, but even then it is far too easy to run software on a machine that is different from the software it should be running.
We've all heard the stories about Diebold machines in the US being preloaded with votes for Bush. Probably some of the stories are true, but what is even more frightening is that there is no way of knowing.
No election is perfect, and a few votes have always been stolen here or there. But we should beware of automating this fraud, giving a single individual in the right place the power not to steal a few votes, but everybody's vote and a whole election.