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by frizlab·3y ago·view on hn ↗
Well I’m still wondering how they are showing a text only to people who submitted something to HN and nobody seems to know either in the thread so at least there’s that…
2 comments
It uses a CSS rule that checks if you have visited the link to submit on hacker news.

https://social.treehouse.systems/@marcan/110503368406970051

wait so you can detect if any of your visitors visited any link before? isn't that a huge privacy risk?
It's probably not being done here , but it's possible to do. The CSS rule is processed in your browser, so it doesn't actually tell the server if you've been to the link, but in theory a website could have some javascript that tries to detect if the CSS rule was activated.
Fair enough. :-)