The most recent update of Invision Power Board (IPB, our forum system) comes integrated with 2-Factor Authentication (2FA) support. We've decided to switch to this having previously relied on an external plugin. Anyone who has previously configured 2FA will need to re-configure it. We apologize for the inconvenience, but on the bright side, this shouldn't be necessary in the future since as long as we stay with IPB.
For those of you who are not familiar with 2FA, it is a way to secure your account even further. In the event someone steals your password, they will be unable to enter your account without also having access to a device of yours that runs Google Authenticator. To set it up, install Google Authenticator on a supported device, scan the bar code found in your account settings, and enter the code that Authenticator displays. If you aren't able to use Google Authenticator or simply don't want to, you can also try WinAuth (thanks to @ReignOfComputer for making me aware of this). Using 2FA is not required, but highly recommended.
If anyone has any questions, feel free to send me a PM, reply to this thread, or ask in our IRC channel.