When you get to the market or organization that you’re looking for—for example, here’s the page for the nonprofit Crossroads GPS—you can click on the ad files shown in the lower left section of the screen to examine specific ad buys. Keep in mind that the overall numbers shown in ProPublica’s application are not totals: they reflect the sum of ad spending that Free the Files volunteers have downloaded, rather than overall spending, and the application only covers several dozen major television markets and not all of the country. For markets not covered in Free the Files, you can go directly to the more cumbersome FCC website, and search by network or affiliate name.

For our story, we decided to examine the group Special OPS OPSEC Education Fund. OPSEC is a group of former special forces officers and CIA officers that has run ads in Virginia markets and on the web accusing President Obama of deliberately leaking national security information for political advantage. PolitiFact has evaluated three of its claims and found them Half True, Mostly False, and False, respectively.

2) Find out whether the sponsor is a nonprofit “social welfare” group

Now that we have the ad and its sponsor, we want to find out the nature of that sponsor. The simplest way to find out whether a group is a PAC, a super PAC, or a nonprofit is simply to Google the group. As ProPublica’s Justin Elliott explained, many groups will state on their website whether they are a nonprofit or a political action committee. The website may also refer to the group’s tax status: a 501(c)(4) organization is a social welfare nonprofit, a 501(c)(6) organization is nonprofit business or trade group, and any kind of committee is likely to be a PAC.

If the group’s website does not describe its tax status, then its filings to the Federal Election Commission will. Enter the name of the group into the FEC’s candidate and committee search form. If the group lists its contributors under a link to “Itemized Individual Contributions,” then it is a political action committee such as a super PAC. If the group only lists several expenditures without any information on its backers—or if it does not show up at all—then it is a “social welfare” nonprofit. For example, you can compare the FEC search results for the pro-Obama super PAC Priorities USA Action—which includes an “Itemized Individual Contributions” link and pie charts showing the group’s receipts and money spent—with the absence of results for its nonprofit sister, Priorities USA, to see the difference in the filings.

In the case of Special OPS OPSEC Education Fund, the procedure was straightforward: the group’s website identifies it at the bottom of the page as “a 501(c)(4) a social welfare organization.” When we looked it up on the FEC website, we did not find any records of expenditures. OPSEC does not list a telephone number on its website, and did not return our email inquiring about its tax status or whether it considered its activities to be political.

3) Find the group’s IRS filings

A few social welfare nonprofits did not apply for IRS recognition at all, a rare but legal course of action than can hamper an organization’s fundraising. But most do, and any group that does seek recognition as a social welfare nonprofit must file a publicly available IRS form called a 1024, which includes a questionnaire about its activities. The questions it must answer include: “Has the organization spent or does it plan to spend any money attempting to influence the selection, nomination, election or appointment to federal, state, or local public office or to an office in a political organization?”

ProPublica’s Kim Barker said that answering “yes” to political activity was believed to raise a yellow flag with the IRS that significantly slowed a group’s recognition as a tax-exempt nonprofit. As a result, ProPublica found, a number of groups answered this question “no,” and then went on to purchase political advertising anyway. “You’re committing perjury if you know at the time that you’re going to spend money on politics, and you fill out a form saying you’re not going to be doing that,” Barker said.

Sasha Chavkin covers political money and influence for CJR's United States Project, our politics and policy desk. He has written for ProPublica, the Center for Public Integrity, and The New York World. Follow him on Twitter @sashachavkin.