Twitter admitted it accidentally reset the passwords of some users as part of a security check-up earlier today.
The company said it was responding to a huge phishing attack on users on Wednesday night, but unintentionally changed the passwords of thousands more users than were affected.
Victims of the phishing attack included technology site Techcrunch, which has 2.5 million followers, and tweeted a link which could have drawn more people in.
Thousands of users of the micro-blogging site received an email warning their accounts had been hacked, and were asked to changed their passwords. The email said:
Concerned tweeters, including comedian David Mitchell, warned followers they may have been hacked, but could not find any evidence.
This prompted numerous users to fear the email from Twitter was a phishing email, and many tweeters said they ignored it.
Twitter cleared up the mix-up by confirming in a blog post it had unintentionally reset passwords in a much larger number of accounts than was intended:
Despite the mistake, Twitter says only a very small percentage of its more than 140 million users had their passwords affected.