So far, the bulk of the money from such non-profit organizations is from conservative groups trying to elect a Republican to the White House and tilt the U.S. Senate to the GOP, The Washington Post reported Tuesday.
Non-profits, unlike super-political action committees, are under no obligation to reveal anyone underwriting their advertising.
"I don't think we've seen these kinds of groups acting so aggressively in election-related activity as we see now," said Richard Hasen, an election law expert at the University of California-Irvine. "This is pure secret money. … The goal is to avoid disclosure."
Non-profits and other tax-exempt groups have spent more than $24 million in the 2012 cycle on advertising naming President Obama or his Republican rivals, accounting for about 40 percent of the money estimated to have been spent on campaign-related ads, a Post analysis of data provided by Kantar Media-CMAG, which tracks ad spending, indicated.
Crossroads GPS, a non-profit backed by GOP political adviser Karl Rove, has spent more than $10 million on ads targeting Obama on the federal deficit, energy policies and other issues in the 2012 cycle.
Americans for Prosperity, a group with ties to the conservative brothers who run the Koch Industries oil-and-gas conglomerate, has spent nearly $7 million on ads targeting Obama, data indicated. Tim Phillips, Americans for Prosperity's president, said he expects total spending will top $50 million in 2012.
Phillips defended keeping donors secret, saying the group works more in public policy and noting donors could be targeted by the Obama administration and liberal groups.
"This administration, and politicians in general, want to seek retribution with people who disagree with them," Phillips said.
Notable deaths of 2014 [PHOTOS]