The DDOS attack against Twitter that began yesterday (Berman Post: Twitter Knocked Out by DDOS Attack) is still going on. This would be in line with the current theory that the attack was targeted at a Georgian blogger to coincide with the anniversary of the Russian invasion (Berman Post: Russia Invades Georgia). After failing to knock out Google, the attackers changed to more vulnerable targets.
"A Georgian blogger with accounts on Twitter, Facebook, LiveJournal, and Google's Blogger and YouTube was targeted in a denial-of-service attack that led to the sitewide outage at Twitter and problems at the other sites on Thursday, according to a Facebook executive.
The blogger, who uses the account name "Cyxymu," (the name of a town in the Republic of Georgia) had accounts on all of the different sites that were attacked at the same time, Max Kelly, chief security officer at Facebook, told CNET News."
More at http://blog.twitter.com/2009/08/adventure-continues.html