Politically active nonprofit organizations outspent super PACs by a nearly 3-to-2 margin in the last national election, according to iWatch News.

A joint probe by the Center for Public Integrity, which operates the iWatch site, and the Center for Responsive Politics found $95-million in political spending by more than 100 501(c)(4) groups during the 2010 campaign, compared with $65-million by super PACs. More than four-fifths of the spending by nonprofits came from conservative groups.

Unlike super PACs — groups that were formed in the wake of the Supreme Court’s January 2010 Citizens United ruling and can raise unlimited political funds from individuals and private groups — nonprofit 501(c)(4)s are not required to disclose their donors. Registered with the Internal Revenue Service as “social welfare” organizations, they are allowed to spend money on politics as long as it is not their primary focus.

So far super PACs have greatly outspent 501(c)(4)s in the 2012 election cycle, but that is expected to change as the primary season ends and the general election campaign begins in earnest, according to the investigative centers.