A security flaw is curently being exploited on Twitter, AKA The Confetti Of The Internet. Reportedly it's just blocking access to accessing user's Twitter home pages and also auto-retweeting the exploit code whenever you move your mouse over parts of the page. However, there have also been reports (not surprisingly) of the exploit being used to forward Twitter users to hard-core porn sites and/or infectious malware sites.
Currently there are thousands and thousands of "infected" Twitter accounts, most notably the account of Sarah Brown, wife of the former British Prime Minister.
Sophos security researchers are warning that it may also lead to endless cascades of spam pop-ups, which compared to malware infections seems like the least of your worries. Sophos recommends that you stay off of Twitter for the immediate future to help prevent/slow the spread of this exploit (and also to protect your computer). We, on the other hand, recommend that you stay off of Twitter indefinitely to help prevent/slow the spread of this exploit (and also to make the world a better place).
This is a "versatile" exploit that works on every OS- Mac and Linux users are affected just like Windows users.