Joseph Goulden has a review in the Washington Times including this info:
... I was not surprised in the 1990s when former KGB Maj. Gen. Oleg Kalugin revealed that the Soviets had worked so closely with Stone in the 1930s that they gave him a codename, "Blin," the Russian term for "pancake." (The term showed up later in the Venona papers as well.) The hateful hounds of the far left, several of whom had worked for Stone's newsletter) brayed loud denials.
But "Spies" documents that Mr. Kalugin was on target concerning Stone. He first appears in KGB files in a 1936 report from Frank Palmer ("Liberal"), identified as "part of the same New York community of pro-Communist radical journalists as Stone." Palmer had been a KGB agent for years, and he was given the OK to recruit Stone. He succeeded, for as he reported a month later, "Relations with 'Pancake' [Stone] have entered the channel of normal operational work." Those last three words denote that Stone had crossed an important Rubicon, from source to spy.
As Mr. Haynes and Mr. Klehr report, based on numerous KGB reports, "Stone assisted Soviet intelligence on a number of tasks, ranging from doing some talent spotting, acting as a courier by relaying information to other agents, and providing journalistic tidbits and data the KGB found interesting."
Pop quiz: guess which McClatchy bigwig admits to being a big I. F. Stone fan.