Twitter, a microblogging service that lets individuals follow each other and update their status, has grown hugely in popularity over the past few months. Obama's campaign team used the service to help co-ordinate supporters during his presidential campaign. He had not been using the account since he won the election.
Other celebrities whose accounts were hacked included Brittney Spears, and Rick Sanchez. Fox News was also hacked by attackers who used the accounts to send malicious messages.
"We are engaged in a full security review of all access points to Twitter. In the meantime, we are taking immediate action," said Twitter in a blog post this week. "First, we are increasing the security of our sign-in mechanism. For added security, we are further restricting access to our support tools."
It has been a bad week for the company in security terms. At the weekend, it was hit by a separate phishing scam, which emailed direct messages to users purporting to come via the Twitter service. When users send direct Twitter messages to each other, they arrive via email to alert the recipient when they are not logged into the service. The mails lured users to sign into a fake Twitter site, thereby giving the users access to their login credentials and allowing them to send direct Twitter messages to others using their accounts.