Twitter was inaccessible for several hours on Thursday afternoon, followed by a period of slowness and sporadic timeouts (and more outright downtime). The company is blaming an "ongoing" denial-of-service (DOS) attack but has not said anything further.
Judging by the timeline of our TweetDeck client, it looks like the problems started right around 2pm BST.
"We are determining the cause and will provide an update shortly," Twitter's staff posted at 2:43pm on the service's status blog.
Then, around 3:49pm, the company posted, "We are defending against a denial-of-service attack, and will update status again shortly."
Around 4:15pm, the status blog post was updated with, "The site is back up, but we are continuing to defend against and recover from this attack." (We were still unable to access Twitter.)
Back in the day, Twitter outages were so commonplace it was only worth reporting when it didn't crash -- as when it stayed afloat during the entire South by Southwest Interactive Festival in 2008. Now, a few million dollars of venture capital later, the service is far more stable.
This is problematic, because 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, such as the Iran election, where more traditional means of broadcasting have been inaccessible or blocked.
Some features of Facebook were also experiencing uptime issues on Thursday -- one reader speculated that login servers may have been down -- which raises the issue of whether a hosting company problem is to blame. Alternately, a denial-of-service attack could have been targeting both high-profile companies.
Facebook is "looking into" the outages, spokeswoman Brandee Barker said in an email to CNET UK's sister site CNET News.
A denial-of-service attack occurs when hackers overload a Web service's infrastructure with data, making its servers slow to a crawl or crash altogether.
There have been a notable number of DOS attacks recently in the social-media space: on Wednesday, URL shortener tr.im claims that one such attack rendered its truncated URLs inaccessible for some time; earlier in the week, blog network Gawker Media was downed by an attack that targeted The Consumerist, a property that it recently sold but still hosts on its servers.
There has been no indication that any of these various attacks are connected. But it's probably not a coincidence that they all coincide with the annual Defcon hacker convention.
Update: As of about 5:30pm, Twitter was back up. And... breathe.