Third Leaker?

The NYT reports that Walter Pincus of the WaPo was told of Valerie Plame by a third administration source .

In that exchange, Mr. Pincus says, "an administration official, who was talking to me confidentially about a matter involving alleged Iraqi nuclear activities, veered off the precise matter we were discussing and told me that the White House had not paid attention" to the trip to Niger by Joseph C. Wilson IV "because it was a boondoggle arranged by his wife, an analyst with the agency who was working on weapons of mass destruction."
SNIP
Mr. Pincus has not identified his source to the public. But a review of Mr. Pincus's own accounts and those of other people with detailed knowledge of the case strongly suggest that his source was neither Karl Rove, Mr. Bush's top political adviser, nor I. Lewis Libby, the chief of staff to Vice President Dick Cheney, and was in fact a third administration official whose identity has not yet been publicly disclosed.

Remember Novak had 2 sources. One was Rove but the other is unknown.
Just how widespread was this smear/cover-up???