Twitter revealed on Friday that "extremely sophisticated" hackers may have gained access to information on thousands of its more than 200 million active users.
"This attack was not the work of amateurs, and we do not believe it was an isolated incident," Bob Lord, Twitter's director of information security, wrote in a blog post.
The attackers, he suspects, may have gained access to usernames, e-mail addresses and encrypted passwords belonging to some 250,000 users.
Twitter has reset the pilfered passwords and has contacted the affected users, advising them to create new ones.
"The attackers were extremely sophisticated, and we believe other companies and organizations have also been recently similarly attacked," the blog said. "For that reason we felt that it was important to publicize this attack while we still gather information, and we are helping government and federal law enforcement in their effort to find and prosecute these attackers to make the Internet safer for all users."
Lord did not name any other suspects in the attack, but noted that The New York Times and The Wall Street Journal both reported this week that Chinese hackers, seeking to monitor their coverage of the country, had infiltrated their computer systems, gaining access to the passwords of high-profile reporters and staff members.
Lord recommended that users rely on a strong password and disable Java in their browsers, citing an advisory from the Homeland Security Department.