Is social media turning socially dangerous?

Flash mobs have become a global phenomenon. After starting out as an oddity, they quickly turned into a tool for organizing people with a cause or for inciting chaos. CBS News correspondent John Blackstone reports that some cities, like San Francisco, are cracking down.

The demonstrators who shut down part of San Francisco's subway during last night's rush hour were brought together with text messages and Internet posts.

They were protesting action taken last week when the rapid transit system blocked cell phone service in four stations. Cell service was turned off to hamper demonstrators' attempts to organize.

"Totalitarian states don't want people to communicate. And the United States is headed toward that kind of attitude, and we gotta stop it!" said protestor Sandy Sanders.

From Egypt to England, governments of every kind are facing the possibilities and perils that come with the growth of social networks and instant messaging.

In Cairo, cell phones and the internet helped demonstrators link up to overthrow a dictator. In London, looters used text messages to identify new targets.

This summer in Philadelphia, gangs used text messaging to quickly organize into so called "flash mobs," that have preyed on downtown businesses.

"We're kind of scarred with the whole flash mob-the city and South Street as well," said Philadelphia bar manager Gart Buck.

Apparently out of nowhere, crowds suddenly appear and run wild. Social media seems to have become anti-social media.

In San Francisco, BART, the transit agency, said cell phones were turned off to keep protestors from putting passengers in danger.

"It'd be the equivalent of people to start protesting on an airplane while you're in flight," said Linton Johnson, chief spokesman for BART.

But critics say the cell phone shut down mirrors attempts in the Middle East to block social media.

"You can't use communication as a tool for social control at home while criticizing foreign governments for doing the same thing," said protester Elijah Sparrow.

This all may be part of our adjustment to new ways to communicate. After all, once even the printing press was considered dangerous.