They leaked

Isikoff suggests where this investigation is now heading (via Atrios):

ISIKOFF: But the problem that people in the White House, Rove among them, may have is how did they know that Valerie Plame, or Wilson's wife worked at the CIA? What we do know is there was a classified State Department report that said this, that was taken by Secretary of State Powell with him on the trip to Africa that President Bush was then on, and many senior White House aides were on.

That classified State Department report appears to have been -- or may well have been the source for the information that Rove and others were then dishing out to reporters. And if that's the case, there still may be -- we don't know yet, but there still may be an instance where classified information was provided to reporters.