How Microsoft and Yahoo are selling politicians access to you

using names, ZIP codes, and other registration information that users provide when they sign up for free e-mail and other services.

The Web giants provide users no notification that their information is being used for political targeting.

In one sense, campaigns are doing a more sophisticated version of what they've always done through the post office—sending political fliers to selected households. But the Internet allows for more subtle targeting. It relies not on e-mail but on advertisements that surfers may not realize have been customized for them.

Campaigns use voter's records to assemble lists of people they're trying to reach—for instance, "registered Republicans that have made a donation," Yahoo Director of Sales Andy Cotten told ProPublica. Microsoft and Yahoo help campaigns find these people online and then send them tailored ads.

http://arstechnica.com/tech-policy/2012/06/how-microsoft-and-yahoo-are-selling-politicians-access-to-you/