Treasury Secretary Jack Lew was first informed in March that there was an investigation into the IRS' screening of nonprofit groups, but did not learn the details of that probe until last week, he said today.

"In mid March, I had had a conversation, just a getting-to-know-you conversation, with the inspector general right after I started, and he went through a number of items that were matters they were working on. And the topic of a project on the 501c3 issue was one of the things he briefed me was ongoing," Lew said in an interview on Bloomberg's "Political Capital with Al Hunt."

"I didn't know any of the details of it until last Friday," said Lew, who was sworn in on Feb. 28. "When I learned about it - from the moment I learned about it, I was outraged," he said.

According to Lew, his predecessor had a similar "heads-up."

Asked if Tim Geithner was aware of the investigation, Lew told Hunt, "Yes. I have to assume, as I was aware of the fact of the matter being subject to a review. That's very different from the substance of the findings."

Lew said that the information he received was "public knowledge."

"It was posted on the IG's website in the fall of 2012," he said. "I believe that … is typically the practice: that an inspector general notify the agencies when matters are opened."

The Treasury inspector general for tax administration, J. Russell George, told lawmakers today that he informed the Treasury Department's general counsel of his audit on June 4 and Deputy Treasury Secretary Neal Wolin "shortly thereafter."