Not all flash mobs are about fun. Chicago and Philadelphia set nighttime curfews this summer to keep teenagers off the streets, after youths began using cell phones to organize mayhem-themed meet-ups. On Aug. 11 in San Francisco, the Bay Area Rapid Transit authority blocked cell service in some train stations to thwart organizers of a rumored protest against police violence. But there was retribution: Anonymous hackers broke into the transit agency's website and forced it off-line.
'I have no problem with folks saying, "Obama cares." I do care.'
PRESIDENT OBAMA, in response to a question in...