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Beware of Twitter: Security Flaw Spreading

Last Updated: Sept. 21, 10:04 AM ET

Sophos has found that Twitter profiles are vulnerable to a 'mouseover' hack, something that many users are already exploiting. Sophos screengrab of Twitter

Security firm Sophos posted a blog entry early Tuesday highlighting a new and potentially dangerous hack of Twitter's Web interface that's begun to make the rounds. It affects only, not third-party clients.

Here's how it works, basically: By putting a bit of JavaScript code ("onmouseover") into a URL in a tweet, a user can cause a pop-up message to emerge when someone hovers a cursor over that link. Sophos notes that right now primary exploiters of the loophole are using it for "fun and games," but that it could potentially be used by spammers or purveyors of malicious code. It appears to work in both the redesigned Twitter Web interface that was launched last week as well as its predecessor.

"Mouseover" hacks are not particularly complicated, and have been implemented in vulnerable e-mail clients for years.

Sophos noted that many Twitter users are playing around with it but that the company hasn't put out an official reaction. Representatives from Twitter were not immediately available for comment.

UPDATE (8:38 a.m. ET): Sophos notes that the exploit is spreading rapidly and that it's now being used to redirect to some hardcore porn sites.

UPDATE (8:51 a.m. ET): The security hole is now being used to "auto-tweet" more mouseover links, and thousands of Twitter users are falling prey to it. For the time being, using a third-party Twitter client may be the safest option.

SS attack identified and patched. 26 seconds ago

UPDATE (9:51 a.m. ET): Twitter says it has identified and is patching the exploit. "We expect the patch to be fully rolled out shortly and will update again when it is," Twitter said on its blog.

UPDATE (10:04 a.m. ET): Twitter says the exploit has been fully patched.

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