Following sporadic access for users throughout most of Thursday morning EST, Twitter posted an update on its status blog (on Tumblr) announcing it had resolved the technical issues and that it was sorry for the downtime. As Twitter's blog post read:
We experienced intermittent issues affecting web and mobile users, globally, between approximately 7:00am and 9:50am PST.
This incident has now been resolved. We apologize to users who were affected by this, and we’re working to ensure that similar issues do not occur.