Ads follow Web users, and get deeply personal - NYTimes.com

For all the concern and uproar over online privacy, marketers and data companies have always known much more about consumers’ offline lives, like income, credit score, home ownership, even what car they drive and whether they have a hunting license. Recently, some of these companies have started connecting this mountain of information to consumers’ browsers.

The result is a sea change in the way consumers encounter the Web. Not only will people see customized advertising, they will see different versions of Web sites from other consumers and even receive different discount offers while shopping — all based on information from their offline history. Two women in adjoining offices could go to the same cosmetic site, but one might see a $300 Missoni perfume, the other the house-brand lipstick on sale for $2...