Though Microsoft, AOL and Yahoo have turned over search data (containing no personally identifiable information, they say) requested by the Justice Department, Google still refuses - "So why is Google the lone holdout?" asks Forbes.com. And it answers: "Perhaps the company really is worried about protecting your privacy. Much more likely: It is worried about protecting itself." Though Google could be protecting trade secrets, including methodologies, the article points to other possibilities.

The government, seeking to revive the Child Online Protection Act (COPA), has received from Google's rivals info about how often certain search terms are used. But that information could be embarrassing to Google, because it would reveal the prevalence of online pornography on the internet - and, as the leading search engine, Google's profiting from the search for such content.

(At least one source also points to the possibility that it might reveal yet another dirty little secret: click fraud.)

Moreover, if COPA were to result in online content filtering, that would hurt Google most in terms of online advertising revenue, on which it is singularly dependent. "Restricting content in any way could hurt Google's carefully burnished image, its 60 percent market share for search queries and its share price," the Forbes article concludes.