Not a fun way to greet the day.
Anti-virus firm Sophos has detail on what had happened:
The Twitter website is being widely exploited by users who have stumbled across a flaw which allows messages to pop-up and third-party websites to open in your browser just by moving your mouse over a link. In a worrying development, messages are also spreading virally exploiting the vulnerability without the consent of users.
Thousands of Twitter accounts have posted messages exploiting the flaw. Victims include Sarah Brown, wife of the former British Prime Minister.
Now, I can't say much about Twitter not acting quickly on this flaw, before I got this blog posted, Twitter support claims to have found and patched the flaw.
It's still safe to follow @georgevhulme on Twitter, for daily security, technology, and business observations.