At 20:49 UTC, our DNS registrar 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.
[UPDATE, 8/28/13: Post updated to reflect that the issue was with our DNS registrar, not our DNS provider.]