Twitter under Denial-of-Service Attack
Aug 6th, 2009 by Johnny

Since approximately 9am Eastern Time, Twitter has been down. Just now on CNBC, they announced that Twitter came out and confirmed they are under a DoS (Denial-of-Service ) attack.
Source: http://www.cnbc.com/id/32297641/
At 12:27PM Eastern Time, CNBC just announced that Twitter is coming back online gradually.
Update provided by NY Times article Attack on Twitter Came in Two Waves