"We’ve identified and are patching a XSS attack; as always, please message @safety if you have info regarding such an exploit," the company said in a status message posted at 6:25 am PT.
Twenty-five minutes later, Twitter updated the message to say that the fix was complete.
The discoverer of the vulnerablity was a Japanese developer by the name of Masato Kinugawa, according to The Guardian. Kinugawa's work was then expanded upon by other developers around the world, several of whom created worms that redirect users to adult Web sites.
Graham Cluley, senior technology consultant for Sophos, a U.K.-based security company, notes that one of the victims was Sarah Brown, wife of the former British Prime Minister. After being hit by the worm, Brown's account included a tweet redirecting visitors to a porn site in Japan.
F-Secure, a security company based in Finland, says that while Twitter may have fixed the problem, it expects problems to continue. "It's perfectly possible that there will be more malicious attacks, possibly combining this technique with browser exploits," the company said in a blog post.
A week ago, Twitter introduced "re-engineered" version of its site, promising a better user experience.