What is privacy? New definition needed.

Position:Credit Card Data

Out of an anonymous set of credit card data from more than 1,000,000 people, how easily can you find one person? Information gleaned from just four transactions uniquely can identify a person 90% of the time, asserts Vivek Singh, assistant professor of library and information science in the School of Communication and Information at Rutgers University, New Brunswick, N.J.

The anonymous set of credit card data from 1,100,000 transactions considered in the study did not include any names, account numbers, or addresses--anything that would be considered an easy identifier. Removing such obvious identifiers is required by the U.S. Privacy Act and the European Union Data Privacy Directive.

"Recently, large-scale data about financial transactions, health records, and taxi trips have been made public for research, which can help fight diseases, or yield better urban planning. They did not have any direct personal information like name, Social Security number, or address, and hence the individuals in these data sets were assumed to not be reidentifiable. This research shows that this expectation is not true in practice," asserts Singh.

"This finding has large implications for what we trust are private sources of information about us. It is relatively easy for anyone, with just a bit of information, to find out very private details about our lives. We therefore need to redefine our current definition of privacy."

Singh explains that movement patterns are linked to the ability to reidentify individuals. "People's movements and behavior patterns uniquely identify them, and thus human behavior becomes very unique very quickly. You can think of it this way: let's say you are standing in a line in front of a store on Monday and you see that there are 100 other people shopping on the same day at the same place. When you go to another store on Tuesday, you will probably only see 30 people from the previous shop. On Wednesday you will only see three of the same people, and by the time you visit the fourth store on Thursday, you are probably the only one from the original 100 you saw at the shop...

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