They are viewed as a threat by most of the adtech ecosystem. Indeed, the loss of profit resulting from the massive adoption of ad blockers was valued at $41.4 billion in 2016 (Adobe/PageFair, The cost of adblocking, 2016).
Ad blocker
Ad blockers are content-filtering and ad-blocking systems that enable users to surf the web without being exposed to any ads. Most of them are web browser extensions, but they can also take other forms (such as a mobile app).