… One of the hallmarks of this campaign is the use of increasingly sophisticated — but not always accurate — data-mining techniques to customize ads for voters based on the digital trails they leave as they visit Internet sites.
It is a practice pioneered by online retailers who work with third-party information resellers to create detailed portraits of consumers, all the better to show them relevant marketing pitches. …
Now some consumer advocates say the proliferation of these trackers raises the risk that information about millions of people’s political beliefs could spread to dozens of business-to-business companies whose names many voters have never even heard. There is growing concern that the campaigns or third-party trackers may later use that voter data for purposes the public never imagined, like excluding someone from a job offer based on his or her past political affiliations. [cont.]
Natasha Singer & Charles Duhigg, New York Times