A new worm is rapidly spreading across microblogging site Twitter according to security firm Sopho.
The worm hacks into Twitter profiles and automatically sends unauthorised Twitter status updates to contacts from the hacked accounts. Users who look at infected profiles are then automatically infected, and unauthorised posts are automatically sent to their contacts.
Possibly infected accounts are creating posts that mention the Twitter profile names of celebrities such as Kutcher and Winfrey, said Graham Cluley, senior technology consultant at Sophos. If the celebrities see the posts and click on the profile names they came from, the infection could spread faster, he said.
Kutcher has more than 1 million people following him on Twitter. "If he were foolish enough to click on one of those, he could be hit and potentially affect a million others," Cluley said.
Cluley wasn't certain whether the accounts of the celebrities themselves had been infected.
Twitter said Friday it was working to fix the problem.
"We're aware of the ongoing spam attack happening on Twitter and we're working to bring it under control," according to a Twitter blog.
The worm spreads by taking advantage of a common Web programming error, called a cross-site scripting vulnerability, on the Twitter website, said Aviv Raff, a computer security researcher. The worm only affects users of the Internet Explorer browser, he said in an interview by instant message.
The worm is a modified version of a series of four cross-site scripting worms that spread last week via Twitter. Called "Mikeyy" or "StalkDaily," the worms started off as plugs for the website StalkDaily.com, which was owned by Mikeyy Mooney. Mooney admitted to creating the worm.
It was revealed on Friday that Mooney was hired by a web company, Exqsoft Solutions, "who appear to have thought this a cheap way of publicity," Cluley said. Mooney may not be responsible for the new worm, but it could be from a script-kiddie looking for a job, or someone looking to take revenge on Mooney.
"It is perfectly possible this is a copycat attack or someone trying to get Mikeyy ... into trouble," Cluley said. Nevertheless, Mooney's original intent was dangerous and he has laid the groundwork for potential legal action against him, Cluley said.
To prevent the worm from affecting profiles, Cluley recommends patching browsers and blocking scripting with a plug-in such as NoScript for Firefox. For those infected, Cluley suggests cleaning up their Twitter profiles and clearing out content they didn't add themselves.
(Robert McMillan in San Francisco contributed to this story.)