Popular social news website Reddit has stopped the spread of a cross-site scripting (XSS) worm that hit the site on Monday.

The XSS worm spread via comments on the site, originally from the account of a user called xssfinder.

Reddit failed to filter out JavaScript in some cases, specifically when a user hovered his or her mouse over a link, a factor the miscreants behind xssfinder's account exploited to run a proof of concept attack.

In an apparent test attack, xssfinder posted a comment linked to malicious scripts on a thread called "Guy on a bike in New York 'high fives' people hailing cabs".

Users reading the comment ended up sending massive amounts of spam comments onto other Reddit threads.

Reddit administrators moved in promptly to close the vulnerability and restore order before things got out of hand. Throughout the confusion the site was never down.

xssfinder's account was deleted soon after the attack began, reports Finnish web security firm F-Secure.

F-Secure's full write-up of the attack, including screenshots, can be found here. One of the comment threads about the assault on Reddit can be found here. ®