http://www.commentarymagazine.com/viewarticle.cfm/i-f--stone--soviet-agent-case-closed-15120
A link for your interest 
It wouldn’t surprise me, and the article lays out a good case.
More on the controversy: 'The Attack on I.F. Stone': An Exchange | Herbert Romerstein | The New York Review of Books
Well, I only had to read as far as the headline to be convinced: