groups cannot -- donor anonymity and less disclosure. >> this, in my view, has a slow corrupting impact on the system, because now you have a vehicle for millions of dollars of secret money. >> reporter: for all parties. but it's lopsided. 85% of the money spent by these groups last year was on the conservative side. >> obama and tester dug the hole. they want people in montana to pay the price. >> reporter: besides airing political ads, these groups say they deserve tax exempt status because they engage in education and advocacy efforts. >> social welfare means the group is working for betterment of our country or our society in some fashion. there are many ways to do this. i see political activity as really a tactic. it's not a purpose of the organization. >> reporter: david keating of the center for competitive politics, who wants less regulation, says these groups are just helping the political dialogue. >> as long as that's not a