Historically, OzBargain was using md5 hashes for storing passwords.Recently, we started storing passwords using the bcrypt algorithm as a proactive measure to improve security. However, since we did not store any plain text passwords, the conversion could only occur whenever a user logged in successfully, on a per-account basis.
In order to eliminate any security risk with using md5, we will be disabling the passwords that have not been converted (i.e. accounts that have not had a fresh login recently). Affected users will need to use the password reset functionality to set a new password. This should only affect users that have not logged in for the last 6-7 weeks and should not affect frequent users.
Please note that this is a proactive measure to improve security, and not a response to a security breach.