Online advertising has become the backbone of the Internet economy by revolutionizing business marketing. It provides a simple and efficient way for advertisers to display their advertisements to specific individual users, and over the last couple of years has contributed to an explosion in the income stream for several Web-based businesses. For example, Google’s income from advertising grew 51.6% between 2016 and 2018, to $\$ $ 136.8 billion. This exponential growth in advertising revenue has motivated fraudsters to exploit the weaknesses of the online advertising model to make money, and researchers to discover new security vulnerabilities in the model, to propose countermeasures and to forecast future trends in research. Motivated by these considerations, this paper presents a comprehensive review of the security threats to online advertising systems. We begin by introducing the motivation for online advertising system, explain how it differs from traditional advertising networks, introduce terminology, and define the current online advertising architecture. We then devise a comprehensive taxonomy of attacks on online advertising to raise awareness among researchers about the vulnerabilities of online advertising ecosystem. We discuss the limitations and effectiveness of the countermeasures that have been developed to secure entities in the advertising ecosystem against these attacks. To complete our work, we identify some open issues and outline some possible directions for future research towards improving security methods for online advertising systems.

中文翻译：

---

在线广告安全：问题、分类和未来方向

通过彻底改变商业营销，在线广告已成为互联网经济的支柱。它为广告商提供了一种向特定个人用户展示其广告的简单而有效的方式，并且在过去几年中为几个基于 Web 的企业的收入流做出了贡献。例如，谷歌的广告收入在 2016 年至 2018 年间增长了 51.6%，至 $\$ $ 1368亿。广告收入的这种指数级增长促使欺诈者利用在线广告模型的弱点赚钱，研究人员发现模型中的新安全漏洞，提出对策并预测未来的研究趋势。基于这些考虑，本文对在线广告系统的安全威胁进行了全面审查。我们首先介绍在线广告系统的动机，解释它与传统广告网络的区别，介绍术语，并定义当前的在线广告架构。然后，我们设计了一个全面的在线广告攻击分类法，以提高研究人员对在线广告生态系统漏洞的认识。我们讨论了为保护广告生态系统中的实体免受这些攻击而开发的对策的局限性和有效性。为了完成我们的工作，我们确定了一些悬而未决的问题，并概述了未来研究改进在线广告系统安全方法的一些可能方向。