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Comment by amelius | Hacker News Reader

Google pretends that it can keep this information behind closed doors without sharing anything with advertisers. But this is not true. Data leaks out, and here is an example of how this might happen.

Let's say you are interested in knowing which people watch a lot of cat videos. And let's pretend these people don't want to publicly share with everybody that they like cat videos. To find these people, you simply start a Google Ad campaign targeted at people who like cat videos. But the ad will be for an unrelated product, for example, coffee pads. Now every time somebody clicks on your ad and perhaps orders your coffee pads, you know that this person likes cat videos.

Ergo, your data is not compeletely safe with Google and it can leak, contrary to what they make us believe.

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Except Google let's you control what ads you're targeted for: https://www.google.com/settings/u/1/ads/authenticated

In your hypothetical, Cat lovers who want to keep that information private can remove 'Pets & Animals - Pets - Cats' from their account targeting. Now they won't see the coffee pad ads.

And no, coffee pad advertisers can't target you based on your pornography viewing habits, HSV cream purchases, or any number of slippery slope examples.

Google had a point if their service was opt-in, but it isn't.

Also, the topic "Cat videos" does not appear, so I have to create it myself? How do I know if Google matches e.g. "Cat" with "Cat videos"?

Further, my other interests may correlate with being a cat video fan, so I have to blank them out as well. But how do I know which they are?

Sorry, but this solution is clearly broken.

(Btw, how does Facebook handle this?)

Advertisers can't target display ads to "Cat videos", they can only target audience topics - i.e. the ones you see and set to your account.

If you think a topic is correlated with one you want to keep private, then you can also keep that topic private by removing it as well. It's well within your own judgement and control, so no, it's not broken.

Facebook lets you do exactly the same thing: https://www.facebook.com/ads/preferences/

Google's ad controls panel says this (after fully disabling targeted advertising):

"Ads you see may still be based on your general location (such as city or county) or recent searches"

Hence, broken.

Also, how about AdWords? As far as I know, you can link any search term (even a competitor's name) to any type of ad you want.

If you purchase something from a location based ad, the advertiser is going to have your billing and shipping information, so that's just splitting hairs at this point.

You're thinking of keyword advertising, not display. AdWords can do both display and keyword advertising, the latter of which is different. Advertisers don't see demographic information about who clicks on their search ads because they can can only target by keywords, so your theory of leaky data doesn't apply there either.

That's also the second time you've moved the goal posts as you've learned more about how online advertising works. Kind of reminds me of this: https://en.wikipedia.org/wiki/No_true_Scotsman

> If you purchase something from a location based ad, the advertiser is going to have your billing and shipping information, so that's just splitting hairs at this point.

Emphasis is on "recent searches", not on the location.

> They can can only target by keywords, so your theory of leaky data doesn't apply there either

Yes, you are more right here (and here only). If ads are only shown when you are actively searching for their keywords, then whether there is a leak is questionable. But an advertiser could still trick one to reveal information, like in a phishing attack, by using keywords unrelated to the ad.

> That's also the second time you've moved the goal posts as you've learned more about how online advertising works.

Thanks for educating me, but my argument still stands. In fact that second time, I placed the goal post back at its original place, since apparently, Google's ad controls do not allow one to turn off ads based on recent searches.

That kind of information leakage would seriously dent Google's business model, which is why I am sceptical of your theory.

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