If you happen to be in your browser looking at twitter.com you may notice that the site is somewhat useless at the moment. Thanks to a JavaScript onMouseOver exploit, a nasty little bug is spreading through the micro-blogging site like wildfire. Simply mousing-over a carefully crafted tweet can redirect your browser to a website with malicious code or, in the case of Sarah Brown (wife of the former British Prime Minister), hardcore porn. The exploit is only affecting twitter.com when viewed in the browser and not third party clients like TweetDeck, Seesmic, or m.twitter.com. If you’re out there and tweeting, be careful.

UPDATE: Bob Lord, Twitter’s security chief, has put up an official blog post explaining exactly what happened this morning. You can read that article here