Hackers hit Twitter, affecting a quarter of a million accounts "This attack was not the work of amateurs, and we do not believe it was an isolated incident," Twitter's director of information security said. Lionel Bonaventure / AFP / Getty Images By Jessica Guynn February 1, 2013, 4:46 p.m. SAN FRANCISCO -- Twitter is the latest target of hackers. The San Francisco company disclosed late Friday that its systems had been attacked by hackers and that nearly a quarter of a million Twitter users were affected. The attack took place over the last week, Twitter said. The unidentified hackers may have had access to usernames, email addresses and other user information. The company has reset the passwords of the affected accounts. It is informing users by email. This week, we detected unusual access patterns that led to us identifying unauthorized access attempts to Twitter user data. We discovered one live attack and were able to shut it down in process moments later," Bob Lord, Twitter's director of information security, said in a blog post. Lord did not tip his hand about who might have been responsible. This attack was not the work of amateurs, and we do not believe it was an isolated incident. The attackers were extremely sophisticated, and we believe other companies and organizations have also been recently similarly attacked," he wrote. A Twitter spokesman declined to comment. The attack comes the same week as major media outlets including the New York Times and the Wall Street Journal disclosed they were victims of hackers. The publications alleged those attacks were a result of their investigative reporting of Chinese officials and blamed the Chinese government. Twitter tries to turn 140 characters into money Hackers attack Western news organizations in China Chinese hackers pose a growing threat to U.S. firms Follow me on Twitter @jguynn.