Around 250,000 Twitter users may have had their accounts compromised by hackers. Today Twitter announced that they have recorded some unusual access patterns that is identified as unauthorized access attempts to Twitter user data. 
Unknown hackers have breached Twitter this week and may have gained access to passwords and other information for as many as 250,000 user accounts.
For security reasons twitter have reset passwords and revoked session tokens for these suspected compromised accounts.
“The attackers may have had access to limited user information – usernames, email addresses, session tokens and encrypted/salted versions of passwords” said Bob Lord ,Director of Information Security, at Twitter.
“This attack was not the work of amateurs and we do not believe it was an isolated incident,” he added.
“The attackers were extremely sophisticated and we believe other companies and organisations have also been recently similarly attacked.”
Twitter have not mentioned that how hackers were able to infiltrate Twitter’s systems, but Twitter’s blog post alluded that hackers had broken in through a zero day vulnerability in Oracle’s Java software.
Update:
Some media portals also relate this attack to Hacktivist Anonymous Group incorrectly, because twitter itself nowhere mention anything about who is attacker
Take a moment now to change your Twitter passwords.