Brown and an unidentified associate did not realize they were being recorded as they discussed their frustrations with how the state pensions issue has played in Whitman's favor.
"Do we want to put an ad out? That I have been warned if I crack down on pensions, I will be that they'll go to Whitman, and that's where they'll go because they know Whitman will give 'em, will cut them a deal, but I won't," Brown said.
A second voice then jumps in and says, "What about saying she's a whore?"
"Well, I'm going to use that," Brown responds on the recording. "It proves you've cut a secret deal to protect the pensions."
Brown campaign spokesman Clifford Sterling confirmed the authenticity of the call, which Whitman's camp has begun to seize on to attack Brown.
"The use of the term 'whore' is an insult to both Meg Whitman and to the women of California. This is an appalling and unforgivable smear against Meg Whitman," said Whitman campaign spokeswoman Sarah Pompei. "At the very least Mr. Brown tacitly approved this despicable slur and he himself may have used the term at least once on this recording."