Duo.com is a plugin that uses Duo.com service to provide simple two-factor authentication for your staff members and clients via the tool of your choice: phone callback, SMS-delivered one-time passcodes, Duo mobile app to generate one-time passcodes, Duo mobile app for smartphone push authentication or Duo hardware token to generate one-time passcodes. Two-factor authentication strengthens access security and provides protection against phishing, social engineering and password brute-force attacks.