
Where have you been, Linda? This has been going on for quite a while now. Started out harmlessly. http://www.makeuseof.com/tag/flash-mob-participate-examples/
...but turned ugly--black 'yoots' coordinating with social media, attacking whites and generally causing mayhem.
http://www.myfoxphilly.com/dpp/news/local_news/caught-on-tape%3A-philadelphia-teen-mob-attack-080811
http://newsone.com/nation/cdixon/teen-mobs-attack-chicago-transit-authority-buses/
http://www.todaystmj4.com/news/local/126825018.html?page=1#respond
...and here's a new twist...organized labor using social media to coordinate flash mobs of strikers.
http://www.cliffviewpilot.com/bergen/2645-striker-flash-mobs-surprising-workers-customers-at-north-jersey-verizon-stores

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