SAN FRANCISCO, July 12 (Xinhua) -- Google+, the social networking service Google unveiled only two weeks ago, is estimated to surpass 10 million users on Tuesday, possibly becoming the fastest growing product in the history of the Internet.

According to Ancestry.com founder Paul Allen (not the co- founder of Microsoft), after passing 10 million users, Google+ " could reach 20 million users by this coming weekend if they keep the Invite Button available."

Allen looks for last names on Google+ and compares them with U. S. Census Bureau data on the popularity of surnames to statistically project the number of Google+ users.

"Since I have been tracking this same cohort of surnames from my first day, I am able to accurately measure growth over time," he said in a blog post on Google+ website.

Google so far has not released any details about the Google+ users or the number of users. Speaking at a press event last Thursday in Sun Valley in the U.S. state of Idaho, former Google CEO and current Executive Chairman Eric Schmidt said there are " millions" of users.

Industry watchers think the estimate may not be completely accurate, but Allen should be capturing the growth trajectory of Google+, which shows that a social network could undergo an exponential growth in its early days.