The machines built by competitor Nedap also broadcast readable signals, as shown by We don't trust voting computers. These have a shorter range (less than 10m). Nedap is working to reduce these emissions, and to remove any readable information from them. These modifications will be tested again before the election.
According to the letter (warning, PDF) written by minister Nicolai, there have been two investigations: one by the AIVD into reading votes remotely, and one by research lab TNO into hacking the machines themselves (changing the software etc.).
For the election, the machines will be sealed more thoroughly than before, and EPROMs will be replaced with ROMs. After the election, several hundred machines will be tested."