Be Daring to Push your Ads Forward: Measuring the (Over)use of Service Workers for Advertising Purposes.

Rich offline experience, periodic background sync, push notification functionality, network requests control, improved performance via requests caching are only a few of the functionalities provided by the Service Workers API. This new technology, supported by all major browsers, can significantly improve users' experience by providing the publisher with the technical foundations that would normally require anative application. Albeit the capabilities of this new technique and its important role in the ecosystem of Progressive Web Apps (PWAs), it is still unclear what is their actual purpose on the web, and how publishers leverage the provided functionality in their web applications. In this study, we shed light in the real world deployment of Service Workers, by conducting the first large scale analysis of the prevalence of Service Workers in the wild. We see that Service Workers are becoming more and more popular, with the adoption increased by 26% only within the last 5 months. Surprisingly, besides their fruitful capabilities, we see that Service Workers are being mostly used for Push Advertising, in 65.08% of the Service Workers that connect with 3rd parties. We Highlight that this is a relatively new way for advertisers to bypass ad-blockers and render ads on the user's displays natively.