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[CNNMoney] Data privacy: What your zip code reveals about you

Every time you mindlessly give a sales clerk your zip code at checkout, you're giving data companies and retailers the ability to track everything from your body type to your bad habits. [...]

That five-digit zip code is one of the key items data brokers use to link a wealth of public records to what you buy. They can figure out whether you're getting married (or divorced), selling your home, smoke cigarettes, sending a kid off to college or about to have one. [...]

In most cases, all that is needed to match the information these data brokers compile with what you buy is your full name — obtained when you swipe a credit card — and a zip code, according to data privacy experts. This allows them to figure out that you are the Sally Smith who lives in Butte, Mont., not the one who lives in Denver, for example. [...]

http://money.cnn.com/2013/04/18/pf/data-privacy/index.html