Two-factor authentication (also known as 2FA) allows you to add a layer of verification to the login process, requiring a different piece of information in addition to your email address and password. The purpose of 2FA is to make it more difficult for an attacker to gain control of your account by requiring a code that is only accessible via a second authentication device. Trello currently supports text message (SMS) and backup codes as 2FA codes.
Please Note: By requiring another layer of verification to access your Trello account, there's an additional responsibility on the user to maintain access to their 2FA device and backup codes.
1. Log in to your Trello acount.
2. Click “Settings” from the drop-down menu that appears when you click your name at the top right of the dashboard.
3. Click “Configure Two Factor Authentication.”
4. Click “Add Two Factor Authentication.”
5. Enter your mobile phone number in the box provided, then click “Send Verification Code.” A code then will be sent to your mobile phone.
6. Enter the code into the Verification Code box, then click “Verify and Update.”
2FA is now enabled! Remember to print out the backup codes provided in case you lose access to your authentication device.
For more information visit: http://help.trello.com/article/993-enabling-two-factor-authentication-for-your-trello-account