My colleague Kashmir Hill congratulated Facebook's Mark Zuckerberg earlier today on his increasingly savvy approach to talking about privacy issues in public. It should be interesting to see him try to talk his way out of this one. The new "Groups" feature that Facebook rolled out yesterday allows users to slice and dice their friends into publicly-visible cliques, recognizing that users don't always want to share something with their entire friend list or just a single recipient. But Sophos security researcher Chet Wisniewski points in his blog to a gaping problem in that feature: Any user can add any of...