Red-faced Facebook executives on Thursday admitted launching a smear campaign against number one rival Google and discredit its privacy practices.

The admission came after an influential blogger revealed his email exchanges with Burson-Marsteller director John Mercurio convincing him to write an article to raise a question about Google's privacy policy on its new feature, the Social Circles.

The blogger Christopher Soghoian, posted that Mercurio detailed in his email Social Circles' features which allegedly claims that Google fail to ask individual users that their profiles and personal data will be shared in the new network. Mercurio even reportedly offered Soghoian in writing the article.

But when Soghoian asked Mercurio who is paying Burson-Marsteller for the smear campaign, the PR executive replied that he cannot reveal his client's identity.

Burson-Marsteller confirmed its involvement in the issue and told Sky News that it regretted the move.

The PR firm said in a statement, "The client requested that its name be withheld on the grounds that it was merely asking to bring publicly available information to light and such information could then be independently and easily replicated by any media."

"Whatever the rationale, this was not at all standard operating procedure and is against our policies, and the assignment on those terms should have been declined."

In a separate statement, Facebook admitted hiring Burson-Marsteller but denied any smear campaign nor authorizing one.

The Facebook statement reads, "Instead, we wanted third parties to verify that people did not approve of the collection and use of information from their accounts on Facebook and other services for inclusion in Google Social Circles - just as Facebook did not approve of use or collection for this purpose."

Facebook said it hired Burson-Marsteller to "focus attention on this issue, using publicly available information that could be independently verified by any media organization or analyst".