A Twitter blog post confirming that accounts had been compromised, suggests that it's likely these are brute force attacks succeeding against user accounts with weak password. Twitter says that they have reset the passwords for the compromised accounts, which should prevent any further spam messages from being sent by the attacker. Earlier this year, an 18 year old US student, that goes by the handle 'GMZ', gained access to several accounts by using a brute force attack and made posts to users Twitter home pages. Accounts that were compromised included Fox News, Britney Spears and Barack Obama.
With the growth in popularity of Twitter, the micro-blogging website is becoming a larger target for spammers, phishers and scammers. Users need to be cautious and use strong passwords to help prevent an account take over. Users who suspect suspicious followers or encounter a spammer can advise Twitter by messaging @spam from their account.