How online marketers target you
— -- Question of the week: How do online marketers use cookies and IP addresses to target me?
Answer: The issue of how companies track us online is in the news— again — after Stanford University grad student Jonathan Mayer observed Google and three other advertising networks circumventing the limits Apple's Safari browser normally sets on the "cookie" files websites can save on the computers of people who visit them.
So it's a good time for a refresher course.
Internet Protocol addresses are the most basic form of identification online. Every device on the Internet — every server, desktop, laptop, tablet, smartphone, anything that can send or receive data online — needs one. But that also means that an IP address identifies nothing more or less than one Internet-connected device.
And since almost all consumer Internet providers reassign IP addresses to their customers as they go on and offline, in practice your IP address only says you're a customer of one ISP or another.
That can allow for a rough hint of your area — explaining why some ads cite your city or county — but nothing further. (When Google Maps pinpoints your laptop's location far more accurately, it does so, with your permission, by analyzing nearby Wi-Fi signals.)
Cookies, in turn, identify a particular browser — even if the computer that browser is running on changes IP addresses.
"First-party" cookies are saved on your computer by the actual site you browsed to; much of the time, they do helpful things to save your preferences or login at that site. "Third-party" cookies — the kind Safari blocks by default — usually come from ad networks, which use them to match ads with potential viewers. (This includes advertisers on USATODAY.com, and, well, pretty much every other major website.)
But they also often provide an inexact match. Hence there are all the people who checked the Google Ads Preferences page (google.com/ads/preferences) in one browser they use and saw that the Web giant thought they were the wrong age, or the wrong gender.
Neither an IP address nor a set of cookie files adds up to the Web equivalent of your Social Security number, something that identifies you uniquely wherever you go.
Marketers can get more accurate data by convincing you to volunteer more information about yourself, either directly or indirectly. Even then, though, few sites will hand over your identity to third parties; Facebook may know an enormous amount about you, but advertisers there can't choose particular users— they can only have their ads shown to people matching particular descriptions.
It's a mistake to spend too much time worrying about the anonymous picture Web advertisers may develop about you. There's so much more data they can collect offline, especially if you happen to use a credit card or have ever bought a house. And a lot of that involves your real name, not a faceless identifier for your computer or the browser on it. See, for example, the New York Times' recent account of how Target was able to market to pregnant women based on their shopping habits in its stores.
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