You’re likely to have come across the term WYSIWYG (what you see is what you get). If not in the past, then sometime likely in your lifetime.
Millions of websites and web-based services use HTTP and HTTP protocols to serve content viewable on a web browser or proprietary applications. The majority of this content can also include online tracking mechanisms that trigger endpoints not visible to the average end user.
In this realm of Internet-things, “what you see isn’t always what you’re actually getting” besides what is designed and rendered to be visible.
These mechanisms I’m referring to are vastly used for different purposes from online tracking, customized advertisements, deep analytics & usability patterns among other things. Popup windows and rampant advertisement banners/images are just symptoms of the problem.
These mechanisms can also be used for nefarious purposes no different than a scam artist trying to take advantage of a tragedy somewhere and pocketing donations they collect.
So remember, the next time you visit a website or use an app, there’s more than what meets the eye.