Although both the Obama and John McCain campaigns are reluctant to discuss details, the ability to identify sympathetic voters based on their Internet habits, and then to target them with ads as they move across the Web, is one of the defining aspects of the 2008 presidential campaign. Digital advertising networks and large Web companies such as Yahoo and Microsoft are using Web behavior -- which news articles people read, which blogs they visit or what search terms they enter -- to target voters who may be sympathetic to a certain cause. Using a method known as "sentiment detection," some companies even boast that they can tell whether the blog you go to is for or against the Iraq war. The advertising techniques, known as "behavioral targeting" and "retargeting," have raised alarms from some privacy advocates, who say no one should unwittingly have their political leanings analyzed as they use the Web, or be tracked for the delivery of political ads. Congress has begun looking into the use of such techniques for commercial advertisers.