On Wednesday, an anonymous hacker going by the name of Hacker Croll posted 13 screenshots to a French online discussion forum, apparently captured while logged into the Twitter account of Jason Goldman, a director of product management with Twitter.
Twitter Cofounder Biz Stone confirmed the breach in a blog post Thursday afternoon. "This week, unauthorized access to Twitter was gained by an outside party," he wrote. "Our initial security reviews and investigations indicate that no account information was altered or removed in any way. However, we discovered that 10 individual accounts were viewed during this unauthorized access."
According to the screenshots, Hacker Croll was able to access account information belonging to high-profile Twitter users such as Britney Spears and Ashton Kutcher. He could also do things such as add or remove featured users, who are suggested to new Twitter members when they sign up.
The hacker may have been able to access information such as e-mail addresses, mobile-phone numbers and a list of the accounts blocked by these users, Stone wrote. "We have personally contacted Twitter users whose accounts were compromised via this unauthorized access," he said.
Hacker Croll claimed to have accessed Goldman's Twitter password by first gaining access to his Yahoo account. "One of the admins has a yahoo account, i've reset the password by answering to the secret question. Then, in the mailbox, i have found her [sic] twitter password," Hacker Croll said Wednesday in a posting to an online discussion forum. "I've used social engineering only, no exploit, no xss vulnerability, no backdoor, np sql injection."
On Monday, Goldman sent a Twitter message saying that his Yahoo mail account had been hacked.
Twitter has had a rash of security problems this year.
In January, another hacker going by the name of GMZ said he was able to gain access to an administrative account by guessing the password of a Twitter support staffer. The password was reportedly an easy-to-guess word: happiness.
GMZ then used that access to take control of 33 high-profile accounts, including those for Spears, U.S. President Barack Obama and Fox News.
Twitter has also been hit with several fast-spreading worm attacks this year that preyed on Web programming flaws on the site.
Although Twitter CEO Biz Stone promised a "full security review of all access points to Twitter" after the January incident, the site's security is "very weak," according to Manuel Dorne, the French blogger and IT project manager who first published news of the most recent Twitter hack.
Stone made a similar promise this time around too. "Twitter takes security very seriously so we will be conducting a thorough, independent security audit of all internal systems and implementing additional anti-intrusion measures to further safeguard user data," he wrote Thursday.
Anyone who tries to log into admin.twitter.com is given a login prompt, and since Twitter user names are already public, attackers have only to guess the password. That could have been what happened with Goldman's account, Dorne said. "Maybe the password was the name of his child or of his wife and the hacker knew it."
These types of attacks, called social engineering attacks by researchers, are effective and commonplace. Last year, a hacker used the same technique described by Hacker Croll to gain access to the Yahoo e-mail account of vice-presidential candidate Sarah Palin.
"We have to be careful and not underestimate social engineering attacks," said Lance James, co-founder of consulting firm Secure Science, via instant message. "If they work for stealing money from banks, it's going to be trivial to hijack social networks such as Twitter."