Anonymous hackers have targeted Twitter this week and gained access to roughly 250,000 user accounts though only "limited information" such as email addresses was compromised, the microblog said on Friday.
Twitter has already reset passwords for affected users, and will notify them soon, it said in a blog post. The cyberattacks come days after the New York Times and the Wall Street Journal revealed they had been the target of a well-coordinated hacking effort.
"This attack was not the work of amateurs, and we do not believe it was an isolated incident," Twitter said. "The attackers were extremely sophisticated, and we believe other companies and organizations have also been recently similarly attacked."