And if you think of it those terms, it's not all that different than the kind of consumer research and targeting that marketers have been doing for years. But here is the difference, while millions have been spent building those big databases or consumer preferences, behavior and history, Facebook is now marrying it to an ocean of personal information, much of which was volunteered without the expectation that it would be siphoned and sold off.

Put another way: just because these brands don't know that "Rebecca Greenfield" saw this ad, doesn't make it that much less creepy when the brands and Facebook mash their hashes and find a way to make ads more intimate. Rajaram doesn't see it that way. He compared what Facebook is doing to direct mail (or email) because a brand has reached out to a certain Facebook user via email to market to them. But, the difference here is in expectations. When signing up for a CVS Extra Care Card before Facebook even existed, I never expected those shopping habits to show up in my Facebook feed. It can also venture on uncomfortable: Do I want my drugstore reflected on a computer screen at work, or in front of friends? Not particularly.

CVS is just an potential source of data. Datalogix and Axciom don't list their clients. Axciom at one point worked with Jet Blue and got in trouble for engaging in "deceptive trading practices." Epsilon, however, has a list of clients that includes Ford, Walgreens, Kraft Foods, GM, and Pepsi Co. That would explain Facebook's car example in its very quiet "Update to Custom Audiences Targeting Tool":

For example, an auto dealer may want to customize an offer to people who are likely to be in the market for a new car. To do this many businesses work with third party companies to better understand who might be in the market for a new car.

As you can see from the list of clients that Axciom works with, the social network could serve up ads ranging from drug store purchases to food to cars all because at some point we formed an email relationship with these retailers in some way.

If all the hashing doesn't assuage privacy fears, those people who really truly don't want these targeted ads, Facebook still lets users opt-out of targeting altogether—though, the process is quite onerous and requires going to the Datalogix, Epsilon or Axciom page and clicking hard to find boxes. Or people can hover over specific ads they don't like and opt-out of that campaign.

Facebook, however, argues that people shouldn't want to opt out—there is an upside to all this data sharing: The ads will be "better." "It’s ultimately good for the users," Gokul Rajaram, product director for ads at Facebook told Sengupta. "They get to see better, more relevant ads from brands and businesses they care about and that they have a prior relationship with."

This article is from the archive of our partner The Wire.

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