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How Facebook Knows When Its Ads Influence Your Offline Purchases

wired.com

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Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#21

Post by chestnut-tree »

Some commentators in this discussion question why anyone would give their phone number to shops when they make a purchase. Yet millions of people give their mobile phone number (and name, date-of-birth and gender) to Google when they sign up for a Google account. And yet the degree of tracking that Google can undertake is an order of magnitude greater than what any individual store can track. Does Google use your mobile number solely for two-factor authentication and absolutely nothing else? Who knows? Google doesn't tell you.

When you can sign in on your tablet/mobile/desktop/TV/thermostat/fridge and who knows what else - how hard can it possibly be to stitch together your spending and consumption habits with all the other data collected about you? In fact, it wouldn't surprise me if those joined-up journeys have already been compiled. It's pretty obvious that the information companies collect about you goes far, far beyond creating a simple "advertising profile".

Companies like Google and Facebook (and others) have no self-restraint when it comes to tracking you and they don't even do it anonymously. How do they get away with it? Because we happily let them.

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#22

Post by dao- »

chestnut-tree wrote: post #21

Some commentators in this discussion question why anyone would give their phone number to shops when they make a purchase. Yet millions of people give their mobile phone number (and name, date-of-birth and gender) to Google when they sign up for a Google account. And yet the degree of tracking that Google can undertake is an order of magnitude greater than what any individual store can track. Does Google use your mob…

Sure. I think the difference is that Google hardly gives you a choice, other than not using their products. Not that this is a great situation. And it still doesn't answer the question why people would give away the same information voluntarily without a direct need.

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#23

Post by moab »

dmurray wrote: post #11
moab wrote: post #8

Earlier quoted context omitted.

Why on earth would you have to brute force all numbers? You can do this optimally: just hash the numbers you see (or get requests for).

So that I can cold call someone who might be interested in my product, even though DataLogix only told me the hash of their phone number.

You've already hashed all numbers on your end, so it's trivial to figure this out (hash the hash?). Hopefully I'm not thinking about this wrong, but it does seem feasible.

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#25

Post by notahacker »

jessriedel wrote: post #5
notahacker wrote: post #4

tldr; it doesn't, but offline vendors that collect your contact information they can anonymously check the proportion of purchasers which might [incidentally?] have been shown their ad on Facebook's network. Only a media buyer with a budget bigger than their brain would assume causality.

Couldn't Facebook easily demonstrate causality by running an RCT? Just randomly select half of a certain demographic to show the ad to, and then show that those users are more likely to make a purchase later.

Theoretically yes, but I think with standard Facebook ad units and regular consumer brands sold in stores they'd be pretty unhappy with the results...

(since probability of giving stores your contact details post purchase and susceptibility to marketing messages pre-purchase are probably positively correlated and Facebook is permanently running concurrent trials of different kinds and being very selective about what they share, any positive effect they did manage to identify should be viewed as an almost certain overstatement of the ads' actual effectiveness anyway)

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#26

Post by tzs »

gcb0 wrote: post #2

...aaand facebook starts to buy news pieces to justify their ad network. this is nothing more than a press-release for their atlas feature. A new low even for wired.

Odd. It seems unusual for a press release to include criticism from the EFF.

How would the article have to have been written for you to not think it was a press release?

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#29

Post by anigbrowl »

berelig wrote: post #16
dao- wrote: post #14

"It has happened to you, and it has probably happened more than once." Umm, no. Why on earth would I give my phone number or email address to random shops? This is crazy. I surely don't want merchants to contact me "about other stuff I might want to buy." This assumption sold as a certainty in this article is somewhat disturbing. Do others from the US feel the same way? (I'm from Germany. Different culture?)

I can only think of a couple of retailers that have asked me for an email address here in Canada (coincidentally both were US companies). I do get asked for my postal code fairly often but that's hardly a personal detail.

You postal code, name and the expiration date on your card is enough to positively ID you in many consumer databases, and by giving it to the retailer you're implicitly granting consent for its use for this purpose.

Re: How Facebook Knows When Its Ads Influence Your Offline Purchases

#30

Post by nly »

logicallee wrote: post #17
dmurray wrote: post #13

Earlier quoted context omitted.

If there is, the 'someone else' would still have to do some rate limiting. Otherwise, once again, I can just run this algorithm for all possible phone numbers.

No, no. Read my link :) The whole point is that the definition of 'zero-knowledge' is that (if you use a zero knowledge interactive protocol) you learn no further knowledge. You are right that the hash-passing is not zero-knowledge. Rather than just verify whether it's in a set, you've accidentally revealed a number. So if you have a set of phone numbers and I have 1 to check if it's in that set, then checking hashes…

Intersecting a set of observed identifiers against another set is an issue Moxie dealt with on the TextSecures blog[0] (for phone numbers at that). He evaluated some ZKP algorithms and basically concluded this problem is hard or impractical today. I imagine an ad/referral network has many of the same real time constraints and scalability issues.

[0] https://whispersystems.org/blog/contact-discovery/

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