Twitter said that it mistakenly reset the passwords of "a large number" of its more than 140 million active users while conducting routine security screening to identify accounts that may have been compromised.

"In instances 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," Twitter said in its blog on Thursday.

It added, "In this case, we unintentionally reset passwords of a larger number of accounts, beyond those that we believed to have been compromised."

Carolyn Penner, a spokesperson for the social-networking site, declined to say how many Twitter accounts were affected by the error.

She said that there had not been a security breach.