Just two days after launching its social e-mail product Buzz, Google has modified the privacy settings for the service to give users greater visibility into how their information and relationships are shared.

The move follows heated criticism over the default setting of the service, which made public people's Gmail contacts with whom they wrote or chatted with the most frequently.

"In particular there's been concern from some people who thought their contacts were being made public without their knowledge (in particular the lists of people they follow, and the people following them)," Todd Jackson, Google's (NASDAQ: GOOG) product manager for Buzz and Gmail, wrote In a blog post explaining the changes.

Under a revised design, Google has made the checkbox to keep a user's Buzz followers private more prominent, though the default setting would still post that information on the person's public Google profile.

"We heard from people that the checkbox for choosing not to display this information was too hard to find, and based on this feedback, we've changed the notice to make it very clear," Jackson said. "We will roll these changes out to all Gmail users later today."

Google has also made it easier to block people with the service by adding a "block" link that allows users to expunge unwanted followers. Previously, users had only been able to block followers who had created public profiles with Google.

Google rolled out Buzz earlier this week at a media event at its headquarters in Mountain View, Calif. The service aims to make Google's e-mail and instant messaging products a more social experience by automatically converting a person's contacts into a social network, inviting users to share photos, videos and links to Web content.

Buzz immediately -- and inevitably -- drew comparisons to Facebook and Twitter, with countless pundits describing the service as Google's effort to best those two popular social sites.

While the initial launch was greeted with widespread skepticism about Google's latest entry into the social space, where it has struggled to gain traction with its Profiles service and fledgling social network Orkut, the conversation turned as the privacy implications of publicizing the contents of one's inbox began to sink in.

Google has said that it continues to gather feedback about the service, and that "we have a long list of improvements on the way."

Jackson said that tens of millions of people had visited the Buzz site since its Tuesday launch, and those who signed up had created more than 9 million posts and comments.