The New York Times Magazine devoted itself this past Sunday to short squibs about famous figures who died in 2008. Among the memorialized deceased was Philip Agee, the CIA agent turned tell-all memoirist, who in 1974 published a list of the spy bureau's active field agents and informants, thus compromising American security and very probably getting a good number of erstwhile comrades killed.  Agee's treason led to the passage in 1982 of the Intelligence Identities Protection Act. Rick Perelstein wrote the Agee entry in the Times Magazine, though I have a quibble over this citation:

The next time Agee showed up in the papers, it was 1974, and he was about to publish “Inside the Company: C.I.A. Diary,” very much against the wishes of his actual former employer — which was not the Olympics section. “I did not write this book for the K.G.B.,” Agee, who worked for a decade as a spook, announced. “I wrote it as a contribution to socialist revolution.”

How generous. Except that he did indeed try to sell American secrets to the K.G.B because the former archivist of the organization, Vasili Mitrokhin, explained in his book The Mitrokhin Archive that in 1973 Agee

approached the KGB residency in Mexico City and offered what the head of the FCD's Counter-Intelligence Directorate, Oleg Kalugin, called 'reams of information about CIA operations'.

Kalugin was skeptical of Agee's goods, however, and turned him down.

Agee then went to the Cubans [says Kalugin], who welcomed him with open arms...The Cubans shared Agee's information with us. But as I sat in my office in Moscow reading reports about the growing revelations coming from Agee, I cursed our officers for turning away such a prize.

Kalugin is now a well-sought lecturer on counterintelligence in the U.S. and a fierce critic of Vladimir Putin. He lives in Maryland. The turncoat who slipped through Kalugin's fingers died in Havana, a long-time guest of the Castro regime, in January.