Foolproof voting systems
The universe can always find a better fool.
Cliches aside, the International Olympic Committee thought their drug testing regime was tamper proof until the Russians decided to do their thing. Anyone big enough and bad enough can get their way if they want, by whatever means they can conjure.
Software is usually very badly written. The more complex the situation, the worse it gets. Anybody who has written software for a living knows this. Expose a typical software system to the wide world and you're in trouble. Most of the problems we've had have resulted from internal systems being networked unwisely for the convenience of administrators or the dictates of marketing. Hey, let's put all these drug dispensing machines on the network so we can monitor them remotely!!! What could go wrong?