Comment by cosmie | Hacker News Reader

Comment by cosmie | Hacker News Reader

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Within Facebook, you can use the event stream collected by your FB Pixel to both define conversion criteria as well as create audiences and define inclusion/exclusion criteria for that audience. When it comes to tracking on pages behind auth, primarily it's for audience building which can be used for

– Cross-sell/Up-sell campaigns. Build an audience based on usage patterns, and create a create a campaign for a complimentary service or higher tier (say, for example, someone clicks the button for a gated feature they don't have access to).

– Suppression lists. If you don't want your campaigns to target existing users, you can build an audience from pixel data on your authenticated pages and suppress against that.

– Lookalike audiences. After you create an audience in Facebook, you can create a "lookalike audience" from that. So even if you aren't actively doing either of the above, you'd derive value from tracking your "best" customers and using it as a seed list for a lookalike audience.

You're also not limited to using the FB Pixel for any of the above. In addition to a browser-side pixel, FB allows you to upload hashed customer information and use those for conversion tracking and audience building. Which used to be completely transparent to end users, but now you're able to see a list of companies that have uploaded your info to FB in this manner (I can't recall where it's buried in the user settings, off the top of my head).

All of that said, it's entirely likely that Backblaze wasn't intentionally sending any of this data to FB to begin with. An insidious aspect of FB's Pixel is that it automatically attaches listeners to a bunch of stuff on the page such as buttons and sends back interactions and associated metadata[1]. The flag to disable this isn't mentioned in the implementation instructions that are generated upfront, and it's actually a fairly uncommon trait for ad pixels. So a typical implementation tends to leave it on out of ignorance rather than make a deliberate determination on whether to use or disable that functionality.

[1] https://developers.facebook.com/docs/facebook-pixel/advanced...

"An insidious aspect of FB's Pixel is that it automatically attaches listeners to a bunch of stuff on the page such as buttons and sends back interactions and associated metadata[1]. "

Um. Holy crap. Is this common knowledge? I don't get shocked easily these days but... wow

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.

[1] https://news.ycombinator.com/item?id=26537140

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