Early error messages said that Twitter was down for maintenance, although it is highly unlikely Twitter would conduct maintenance activities during the middle of a business day. Many suspected it had something to do with changes made to the Connect tab on the top bar, which has now been renamed Notifications.
By 2:30 p.m. EDT Twitter acknowledged its services were down and sent out a post outlining the real cause for the outage.
"During a planned deploy in one of our core services, we experienced unexpected complications that made Twitter unavailable for many users starting at 11:01 am. We rolled back the change as soon as we identified the issue and began a controlled recovery to ensure stability of other parts of the service. The site was fully recovered by 11:47 am PDT. We apologize for the inconvenience."
While most users have regained access to Twitter, some users are still having issues accessing the site and certain third-party clients, such as Hootsuite and Twitterfall, are still having trouble accessing the service.