But companies are now getting smarter in tracking people's online behavior across devices. Google and Facebook are refining their techniques for connecting the ads people see online to whether they bought items in a physical store. Facebook's recently relaunched Atlas system lets partnered advertisers leverage Facebook members' data across the wider Internet.
To preserve privacy, the recommendation to delete cookie files doesn't really apply anymore, because more tracking is being done on mobile where cookies don't work.
Perhaps instead people should contact companies like Google and Facebook, and ask them to be more transparent about exactly what data they sell, and to whom, Turow said.
Government agencies like the U.S. Federal Trade Commission can help to preserve privacy too, or at least help companies become more transparent. Snapchat entered into an agreement earlier this year with the FTC to settle charges that it deceived users about the amount of personal data it collects.
Pew's Rainie said the nonprofit would explore more of the responses people say they can take in the group's upcoming surveys.
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