Twitter tells Buzzfeed FWD:
Today's outage is due to a cascaded bug in one of our infrastructure components. We'll provide updated information soon.
Twitter then clarified in a tweet:
So, not much. But if you read between the lines and, like, realllly squint, this looks more like a low-level failure than a problem in Twitter's own codebase — perhaps something that originated in its data centers, or in a piece of third-party software. Considering that we haven't even been getting the Fail Whale, this must be a fairly essential disturbance.
Meanwhile, a hacker group nobody has heard of is claiming the outage is a result of a DDoS attack. This, for now, sounds very unlikely. Twitter is not the kind of site you an easily take down by loading it a bunch of times. That's what it's for.
In any case, Buzzfeed's offices today have been like the streets of New York during a blackout. Lots of hugging and laughing. A little crying. A few of us even joined Plurk.
UPDATE: The full explanation, according to Twitter:
Not how we wanted today to go. At approximately 9:00am PDT, we discovered that Twitter was inaccessible for all web users, and mobile clients were not showing new Tweets. We immediately began to investigate the issue and found that there was a cascading bug in one of our infrastructure components.
This wasn’t due to a hack orour new office or Euro 2012 or GIF avatars, as some have speculated today. A “cascading bug” is a bug with an effect that isn’t confined to a particular software element, but rather its effect “cascades” into other elements as well. One of the characteristics of such a bug is that it can have a significant impact on all users, worldwide, which was the case today. As soon as we discovered it, we took corrective actions, which included rolling back to a previous stable version of Twitter.
There's more on the Twitter blog. I'm just glad it (allegedly) wasn't the GIF avatars' fault. #GIFLife forever.