Do trackers track you already by preconnect and or dns-prefetch?


I read this tweet showing the number of trackers blocked by Ghostery for a certain site. Then I got curious and opened that specific page in Safari on my Mac trying to compare the blocked lists. There I get only three blocked assets.

But if I take a closer look at the source code I already see those:

So I wonder if trackers are already able to track visitors of a particular page by those preconnects and or dns-prefetches? Cuz most of the listed trackers in the second screenshot are also in Betters curated list. But just based on the blocks from the console shown in the first screenshot I would assume quite a few are missing and are just passed through? Running Better 2017.1 on MacOS 10.11.6 and Safari 10.1. Cheers r.


Ooh, those sneaky wotsits. I’m not 100% sure what’s going on with those preconnect URLs, but looking at their page, I can see they are embedding the trackers into the HTML page to stop them from being blocked by blockers that block third-party trackers.

I’ve opened an issue, and we’ll look into it:


came across their site via that tweet showing a Ghostery blocklist ( but when comparing blocked sites on the screenshot with the ones in my own console i’ve noticed discrepancies. especially since a few of the hagebaumarkt trackers are in Betters list but not shown in the console. so thanks for investigating :slight_smile: