The outage appears to be as a result of a sustained and ongoing cyberattack by the government of Iran:
http://www.cnbc.com/id/49109110
http://openchannel.nbcnews.com/_news/2012/09/20/13990206-officials-see-iran-not-outrage-over-film-behind-cyber-attacks-on-us-banks?chromedomain=worldnews&lite
