I'm not really sure if it's common knowledge, but I'd say it's less common then it should be. I went ahead and made a top level comment[1] with some info about controlling data disclosure to FB's Pixel in case it's helpful to others.
In the analytics space, you traditionally had to:
– Initialize a tracking object on page load
– Explicitly call methods on that tracking object when you wanted to actually send a hit
This is how it works for Adobe Analytics and Google Analytics historically. Many of the newer analytics providers instantiate auto-listeners, which gave them an edge on the out-of-the-box analytics features. And Google Analytics 4 (the newest release), also does this.
So it's not unheard of for site analytics. And a quick glance at a particular provider's website can usually make it obvious if this is occurring, based on the advertised features.
Ad pixels tend to be different though. You create a conversion event within the ad platform, and you're given a snippet of code to fire when that specific event occurs, which both instantiates the tracking object and calls the tracking method with the conversion event's configuration details.
Facebook's pixel works far more like a modern analytics library than an ad pixel. It vacuums up the hit data from the site and the marketer is able to sort it out after the fact in Facebook's interface and use what they want from it. Marketers working within Facebook can see this is happening because they set up the conversions and audiences against the hit data, but that's "just the way things work" in Facebook so they think nothing of it. Marketers coming from other channels will notice how different it is, but won't realize what's actually happening nor the implications behind it. Devs would realize pretty quickly what's happening after a few minutes exposure to the FB Pixel interface and it'd trigger a red flag for them, but that's marketing's territory and all devs see are the snippets provided for implementation. So the only time most people become aware of it is if marketing has someone technical working directly within FB's interface or if the person tasked with implementation has a reason to dig into Facebook's dev documentation rather than just plop the snippet on the page like they were told.
In the analytics space, you traditionally had to: – Initialize a tracking object on page load – Explicitly call methods on that tracking object when you wanted to actually send a hit
This is how it works for Adobe Analytics and Google Analytics historically. Many of the newer analytics providers instantiate auto-listeners, which gave them an edge on the out-of-the-box analytics features. And Google Analytics 4 (the newest release), also does this.
So it's not unheard of for site analytics. And a quick glance at a particular provider's website can usually make it obvious if this is occurring, based on the advertised features.
Ad pixels tend to be different though. You create a conversion event within the ad platform, and you're given a snippet of code to fire when that specific event occurs, which both instantiates the tracking object and calls the tracking method with the conversion event's configuration details.
Facebook's pixel works far more like a modern analytics library than an ad pixel. It vacuums up the hit data from the site and the marketer is able to sort it out after the fact in Facebook's interface and use what they want from it. Marketers working within Facebook can see this is happening because they set up the conversions and audiences against the hit data, but that's "just the way things work" in Facebook so they think nothing of it. Marketers coming from other channels will notice how different it is, but won't realize what's actually happening nor the implications behind it. Devs would realize pretty quickly what's happening after a few minutes exposure to the FB Pixel interface and it'd trigger a red flag for them, but that's marketing's territory and all devs see are the snippets provided for implementation. So the only time most people become aware of it is if marketing has someone technical working directly within FB's interface or if the person tasked with implementation has a reason to dig into Facebook's dev documentation rather than just plop the snippet on the page like they were told.
[1] https://news.ycombinator.com/item?id=26537140