Is artificial intelligence vulnerable to hacking? The paper The Limitations of Deep Learning in Adversarial Settings explores how neural networks might be corrupted by an attacker who can manipulate the data set that the neural network trains with. The authors experiment with a neural network meant to read handwritten digits, undermining its reading ability by distorting the samples of handwritten digits that the neural network is trained with.

I'm concerned that malicious actors might try hacking AI. For example


Fooling autonomous vehicles to misinterpret stop signs vs. speed limit.
Bypassing facial recognition, such as the ones for ATM.
Bypassing spam filters.
Fooling sentiment analysis of movie reviews, hotels, etc.
Bypassing anomaly detection engines.
Faking voice commands.
Misclassifying machine learning based-medical predictions.


What adversarial effect could disrupt the world? How we can prevent it?
AI is vulnerable from two security perspectives the way I see it: 


The classic method of exploiting outright programmatic errors to achieve some sort of code execution on the machine that is running the AI or to extract data.
Trickery through the equivalent of AI optical illusions for the particular form of data that the system is designed to deal with.


The first has to be mitigated in the same way as any other software. I'm uncertain if AI is any more vulnerable on this front than other software, I'd be inclined to think that the complexity maybe slightly heightens the risk.

The second is probably best mitigated by both the careful refinement of the system as noted in some of the other answers, but also by making the system more context-sensitive; many adversarial techniques rely on the input being assessed in a vacuum.