In an unprecedented step, Egypt has closed all of its Internet connections including Twitter. This comes in reaction to widespread demonstrations and rioting by its citizens and is seen as an attempt to prevent opposition from using Internet social media to arrange rallies and to communicate with member activists.
This "kill switch" option was also matter of some debate in the United States, when legislation was proposed giving the president power over privately owned computer systems during a “national cyber-emergency,” and prohibiting any review by the court system. The proposed bill is, Bill S.3480, or the Protecting Cyberspace as a National Asset Act (PCNAA). It authorizes President Obama to have the power to shut down the internet, presumably in cases of national emergencies and/or cyber attacks. For more information about this bill try this link.
In Egypt we can find a frightening demonstration how this power could be legally abused in the wrong hands.