The Syrian Electronic Army just claimed that it has taken over Twitter's domain registration. Several public Whois listings showed sea@sea.sy as the contact information for Twitter.com but are now back to normal, which indicate that they may not be bluffing.

There are also reports of users experiencing problems. Earlier today, SEA (or someone) took over the NYTimes' domain.

Both the NYTimes.com and Twitter.com show registration through the same registration service.

Registrar: MELBOURNE IT, LTD. D/B/A INTERNET NAMES WORLDWIDE
Whois Server: whois.melbourneit.com
Creation Date: 18-JAN-1994
Updated Date: 27-AUG-2013
Expiration Date: 19-JAN-2014

Embedded tweets also broke.

Here's the official word from Twitter. The domain records were modified, but your data isn't compromised:
At 20:49 UTC, our DNS provider experienced an issue in which it appears DNS records for various organizations were modified, including one of Twitter’s domains used for image serving, twimg.com. Viewing of images and photos was sporadically impacted. By 22:29 UTC, the original domain record for twimg.com was restored. No Twitter user information was affected by this incident.