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Ask HN: How does Facebook know what I buy on Amazon or vice versa?

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Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#12
I am working at FB but not in ads or related team. But I had talked to a person who is directly working on it.

Amazon is different to other AD buyers. Amazon does not want FB to know what customers are doing on its own site, so there is no FB tracker on Amazon at all. However, Amazon can choose what ad to deliver to you on FB backed up by its own team.

Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#14
post #9

I have had similar experiences. Others have already mentioned some cross-browser fingerprintig techniques. One of the worst that many people don't know about is that browsers hand over your local IP. Check this proof of concept: http://net.ipcalf.com/ The media device IDs the browsers provide look even worse: https://jsfiddle.net/u4n4s296/ I am not sure if these are unique to the device type (for example a certain so…

Whoa, for a moment I felt pretty sure you would be mistaken. Hadn't read about this particular vulnerability before.

Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#17
post #9

I have had similar experiences. Others have already mentioned some cross-browser fingerprintig techniques. One of the worst that many people don't know about is that browsers hand over your local IP. Check this proof of concept: http://net.ipcalf.com/ The media device IDs the browsers provide look even worse: https://jsfiddle.net/u4n4s296/ I am not sure if these are unique to the device type (for example a certain so…

Love the comment. "In Chrome and Firefox your IP should display automatically, by the power of WebRTCskull."

Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#18
post #9

I have had similar experiences. Others have already mentioned some cross-browser fingerprintig techniques. One of the worst that many people don't know about is that browsers hand over your local IP. Check this proof of concept: http://net.ipcalf.com/ The media device IDs the browsers provide look even worse: https://jsfiddle.net/u4n4s296/ I am not sure if these are unique to the device type (for example a certain so…

Haha, wow. What is wrong with people nowadays, that they think this is reasonable behavior...

Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#19

I am working at FB but not in ads or related team. But I had talked to a person who is directly working on it. Amazon is different to other AD buyers. Amazon does not want FB to know what customers are doing on its own site, so there is no FB tracker on Amazon at all. However, Amazon can choose what ad to deliver to you on FB backed up by its own team.

OP says they have different email addresses for Amazon and FB. How would Amazon know which user to target ads on FB in this case?

Re: Ask HN: How does Facebook know what I buy on Amazon or vice versa?

#20
post #9

I have had similar experiences. Others have already mentioned some cross-browser fingerprintig techniques. One of the worst that many people don't know about is that browsers hand over your local IP. Check this proof of concept: http://net.ipcalf.com/ The media device IDs the browsers provide look even worse: https://jsfiddle.net/u4n4s296/ I am not sure if these are unique to the device type (for example a certain so…

Interestingly, this doesn't seem to work for me if I have uBlock Origin enabled. However, nothing is logged as blocked in uBO, so I can't tell what it's doing to break it.
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