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Ask HN: How is this 'cross advert' possible?

1 points by bikamonki ↗ HN
I was logged into FB on one tab and then searched for a bike on Amazon, on a new tab. I think that I was not logged into Amazon. A couple of hours later I logged back into FB and there was this ad: http://www.grupster.com/crossadvert/fb_ss_blrd.png.

How do they make this work? Cookies? Do I have adware on my laptop/browser? Do FB and Amazon share traffic data? All of the above?

4 comments

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greenyoda
It's also possible that it was a coincidence.
bikamonki
If it was the first time, maybe. I've seen it also when browsing my local newspaper site: ads with sites/products I use/search for.