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Four purchases to identify an individual

Study finds it is easy to spot almost all of us just through our card spending

According to a study released in the journal Science, a crafty user has a 94 percent chance of tracking all of your purchases with three pieces of extra information — one receipt, an Instagram of your lunch, a Tweet about the new shoes you bought or Facebook post tagging the bar where you went for happy hour.

Credit card data isn´t quite as anonymous as promised, a new study finds. Scientists showed they can identify you with more than 90 percent accuracy by looking at just four purchases, three if the price is included — and this is after companies "anonymized" the transaction records, saying they wiped away names and other personal details. The study out of MIT, published Thursday in the journal Science, examined three months of credit card records for 1.1 million people.

Just four bits of information gleaned from a shopper´s credit card can be used to identify almost anyone, suggesting that even anonymous big data sets can breach individual privacy.

The study crunched three months of credit card records for 1.1 million people in an unidentified industrialized country. Ninety percent of individuals could be uniquely identified using just four pieces of information, such as where they bought coffee one day, or where they purchased a new sweater or pair of shoes.

In other words, credit cards use was just as reliable at identifying someone as mobile phone records, the study said. Knowing the price of a transaction could boost the risk of re-identification by 22 percent.

The study also revealed that it´s easier to identify women using the technique, though the researchers can´t yet explain why.

The study goes to show that a sense of privacy though anonymized data is somewhat of an illusion. Even without any of our details to identify us, all it takes is careful use of metadata—in this case, our shop visits—to identify us completely

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