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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?

#21

Post by thisismine »

rajathagasthya wrote: post #19
captainhcg wrote: post #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.

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?

Cookie is a thing.

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

#22

Post by throwaway613834 »

anowlcalledjosh wrote: post #20
TekMol wrote: 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.

Same with Privacy Badger. I think it's the "Prevent WebRTC from leaking local IP address" option in the General Settings, except that mine is unset, yet they say the "Default options" protect me so I'm not sure if it's partially set by default anyway.

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

#23

Post by icebraining »

js7745 wrote: post #10

They use the Facebook Pixel https://www.facebook.com/business/a/facebook-pixel They segment users that visited each product on Facebook with a custom audience and then create ads for similar products that they show you. This is all done programmatically.

How would that work across different browsers?

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

#24

Post by icebraining »

TekMol wrote: 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…

In Firefox, the media device IDs are different for each site (origin): It is un-guessable by other applications and unique to the origin of the calling application. It is reset when the user clears cookies (for Private Browsing, a different identifier is used that is not persisted across sessions).

https://developer.mozilla.org/en-US/docs/Web/API/MediaDevice...

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

#25

Post by __abc »

This is all fairly straight forward however, what blows my mind is Facebook makes recommendations of friends that I've NEVER had any digital interaction with.

For some reason it picked up the kid who stocks the craft beer at my local family run grocer. Literally only talked to the kid face-to-face. No phone number, no texting, no contact entry (not that I share those with Facebook anyways).

That made the hair on the back of my neck stick up when that happened.

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

#26

Post by ars »

thisismine wrote: post #21
rajathagasthya wrote: post #19

Earlier quoted context omitted.

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?

Cookie is a thing.

It's not cookie, it happens across different browsers. It's IP based.

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

#27

Post by ars »

molestrangler wrote: post #16

If you stay logged in on FaceBook and browse & search other sites they know. Only login when you need it the service, then logout and delete cookies.

That doesn't make any difference. It tracks across browsers that are not connected in any way except IP.

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

#28

Post by ars »

jayess wrote: post #13

Another reason to install ublock and add the social tracking filters.

That would not help. Amazon knows what you looked at because you did it on their site.

It's not Facebook tracking you, it's Amazon.

It's also not Facebook giving you the ad, it's Amazon. So technically not a privacy violation.

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

#29

Post by eknkc »

__abc wrote: post #25

This is all fairly straight forward however, what blows my mind is Facebook makes recommendations of friends that I've NEVER had any digital interaction with. For some reason it picked up the kid who stocks the craft beer at my local family run grocer. Literally only talked to the kid face-to-face. No phone number, no texting, no contact entry (not that I share those with Facebook anyways). That made the hair on the…

Maybe he searched and looked you up on Facebook and it's somehow enough signal to suggest him?

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

#30

Post by darylfritz »

thisismine wrote: post #21
rajathagasthya wrote: post #19

Earlier quoted context omitted.

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?

Cookie is a thing.

OP also said they used two completely different browsers
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