According to Twitter’s blog post, they have been getting hit pretty hard this week by some very sophisticated attacks and may have had up to 250k users information compromised. Twitter has:
indicated that the attackers may have had access to limited user information – usernames, email addresses, session tokens and encrypted/salted versions of passwords – for approximately 250,000 users.
Twitter has reset the passwords to those accounts and revoked the session tokens. Twitter has said that this is not the work of any rank amateurs either and that is a very sophisticated attack that would be on the same level as the NY Times and Wall Street Journal experienced this week also. Those attacks are reportedly being carried out by hackers in China but Twitter has not directly indicated that this was the case here. They did decide to go public with the attacks in an attempt to help gather information.
So if you try to log in to Twitter and you password needs to be reset you might have been one of the small percentage affected by the hackers today.