From Twitter's blog

"The issue with these 33 accounts is different from the Phishing scam aimed at Twitter users this weekend. These accounts were compromised by an individual who hacked into some of the tools our support team uses to help people do things like edit the email address associated with their Twitter account when they can't remember or get stuck. We considered this a very serious breach of security and immediately took the support tools offline. We'll put them back only when they're safe and secure."

Stephen Fry hit by Twitter ID hack: http://www.itworld.com/security/60075/stephen-fry-hit-twitter-id-hack
Rick Sanchez' Twitter Hacked: http://www.mediabistro.com/webnewser/personalities/rick_sanchez_twitter_hacked_104818.asp
Twitters Response: http://blog.twitter.com/2009/01/monday-morning-madness.html
Twitter phishing scams - Not so tweet: http://blogs.computerworld.com/twitter_phishing