Some people logging onto Twitter on Thursday were greeted with word that their passwords were reset due to concerns their accounts may have been breached by hackers.
The San Francisco-based one-to-many text messaging service said the routine security precaution was accidentally applied to more users than intended.
Twitter did not specify the number of accounts involved.
"When we believe an account may have been compromised, we reset the password and send an email letting the account owner know this has happened along with information about creating a new password," Twitter told AFP.
"In this case, we unintentionally reset passwords of a larger number of accounts, beyond those that we believed to have been compromised."
Twitter apologized for any confusion caused by password resets. Internet security specialists advise people to regularly change passwords on accounts to thwart hackers.
Twitter on Thursday also posted a "bug alert" telling users that it was working to fix problems with disappearing "tweets" and direct messages at the service.
"Our engineers are hard at work to solve these issues," the Twitter support team said in a blog post.