With rapid progress and great successes in a wide spectrum of applications, deep learning is being applied in many safety-critical environments. However, deep neural networks have been recently found vulnerable to well-designed input samples, called \textit{adversarial examples}. Adversarial examples are imperceptible to human but can easily fool deep neural networks in the testing/deploying stage. The vulnerability to adversarial examples becomes one of the major risks for applying deep neural networks in safety-critical scenarios. Therefore, the attacks and defenses on adversarial examples draw great attention. In this paper, we review recent findings on adversarial examples against deep neural networks, summarize the methods for generating adversarial examples, and propose a taxonomy of these methods. Under the taxonomy, applications and countermeasures for adversarial examples are investigated. We further elaborate on adversarial examples and explore the challenges and the potential solutions. Adversarial Examples: Attacks and Defenses for Deep Learning