The number of people sharing personal information online and spending more time communicating via social networking sites is growing by quantum leaps. This summer Facebook membership soared over 500 million — a meteoric rise from its mere 1 million members in 2005. The “micro-blogging” social site Twitter — where posts must total 140 characters or fewer — recently passed the 140-million-member mark. The rising dominance of social media sites means that users' lives — both online and offline — will be increasingly more transparent, with full information about their doings available for everyone to see, including parents and bosses, according to Facebook founder and CEO Mark Zuckerberg. For some, the new world of “radical transparency” will increase human understanding and encourage honesty and accountability. But some lawmakers and scholars concerned about losing older notions of privacy warn that more should be done to help individuals control how much of their personal data is publicly accessible.