UPDATE 12:00 P.M.
Twitter is back up and running. As per their service status page the outage was due a new change they were making live.
Here is their explanation below.
Update [12:12pm PDT]: During a planned deploy in one of our core services, we experienced unexpected complications that made Twitter unavailable for many users starting at 11:01am. 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 11:47am PDT. We apologize for the inconvenience.
Users are reporting that Twitter is down, and no activity has been seen for at least an hour.
The outage appears to be affecting the service across the mobile app and website.
Some outlets are reporting that the service went down around 11 a.m. on Tuesday.
One of the last major Twitter outages occurred back in September of 2013.
The photo above is the current message on the twitter.com website.
We will have more details as they become available.