Twitter on Thursday urged all users to change their passwords after it found a bug that had left some passwords readable in an internal computer system. The bug was able to bypass the technology the company uses to disguise passwords so that its employees cannot see them.

The microblogging website said it had fixed the problem and had not found any indication of a breach or misuse by anyone. However, it asked users to consider changing their passwords “out of an abundance of caution”.

A blog post by Twitter did not say how many passwords were affected, but an unidentified official told Reuters that the number was substantial and the passwords were exposed for “several months”. The bug was discovered a few weeks ago, and Twitter reported it to some regulators, the official said.

“We are very sorry this happened,” the blog post said. “We found this error ourselves, removed the passwords, and are implementing plans to prevent this bug from happening again.”