Twitter Gets A denial-of-service attack

Twitter was inaccessible for several hours on Thursday morning, followed by a period of slowness and sporadic time-outs (and more outright downtime). The company is blaming an "ongoing" denial-of-service attack but has not said anything further. Facebook has also confirmed that it was targeted by a DoS attack that rendered some of its features slow or non-functional.
"We are determining the cause and will provide an update shortly," Twitter's staff posted at 6:43 a.m. PDT on the service's status blog.
Then, around 7:49 a.m. PT, the company posted, "We are defending against a denial-of-service attack and will update status again shortly."
Around 8:15 a.m., the status blog post was updated with "The site is back up, but we are continuing to defend against and recover from this attack." (I still was unable to access Twitter.)
Way back when, Twitter outages were so commonplace that it was worth reporting when it didn't crash--as when it stayed afloat during the entire South by Southwest Interactive Festival in 2008.
Twitter wants to establish itself as a communications standard rather than just a social-media brand. It's been a crucial platform for information exchange in the face of global events where more traditional means of broadcasting have been inaccessible or blocked.