Today, Twitter issued an alert to users prompting them to change their passwords after the discovery that some users' passwords had been recorded in plain text in a log file accessible only by Twitter employees. In a message pushed to most Twitter users, the company stated:

We recently identified a bug that stored passwords unmasked in an internal log. We have fixed the bug, and our investigation shows no indication of breach or misuse by anyone. Out of an abundance of caution, we ask that you consider changing your password on all services where you've used this password.

In a blog post, Twitter Chief Technology Officer Parag Agrawal wrote that Twitter uses the bcrypt hashing function, based on Bruce Schneier's Blowfish encryption algorithm, to store mathematical representations of passwords. "This allows our systems to validate your account credentials without revealing your password," Agrawal noted. "This is an industry standard."

But because of a coding bug, Agrawal explained, "passwords were written to an internal log before completing the hashing process. We found this error ourselves, removed the passwords, and are implementing plans to prevent this bug from happening again."

The alert comes two days after a similar bug affected the passwords of some users of the code-sharing site GitHub. GitHub also found an internal log had recorded passwords before hashing and alerted affected users.

While the odds of passwords actually being exposed to someone outside Twitter or GitHub in both of these cases is relatively low, the possibility exists that someone could have intercepted the unencrypted passwords as they were written to log files or obtained a copy of the log somehow. So if you're a Twitter user or are one of the GitHub users who received a notification, you should change your password on the affected services—as well as anywhere else you may have used the password. If you have implemented two-factor authentication for Twitter, the risk of access to your account is much lower, but someone who has access to the account data might use it to attempt to gain access to email and other Web accounts.