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Twitter says over 250,000 accounts are effected, and in an attempt to secure these accounts, have reset token access and password data for each of the accounts affected. These accounts will receive an email from Twitter regarding the issue.
"If your account was one of them, you will have recently received (or will shortly) an email from us at the address associated with your Twitter account notifying you that you will need to create a new password. Your old password will not work when you try to log in to Twitter." States the blog post.
source: Twitter Blog