Tracking Shady Money Trail Behind Mystery Attack Ads

As a result of the Supreme Court's ruling, groups such as Americans for New Leadership and Concerned Taxpayers for America have come out to take advantage of the new rules. Some of these groups are known as 501c4's, which is a tax designation; others are simply referred to as "super-PACS."

Who is getting most of the money, and why now? Peter Overby, who covers money in politics for NPR, tells Guy Raz that court decisions such as Citizens United changed all of the rules.

These new rules "let corporations and unions spend as much as they want to attack or promote candidates," Overby explains. "They can't give money to the candidates, but they can be in the battle, running attack ads, which is what most of these groups do."