It was successful because they were able to detect if someone voted CDA (ChristenDemocratisch Appèl) because the "è" sent out a different radio wave that was detectable from a distance and broke voting secrecy. The main point, that electronics are orders of magnitude harder to secure because they are inherently more complex and less transparent than simple solutions like ballot boxes and voting on paper, is still not well understood in society and even not in the hacker community as you can read in most of the comments here.