Duo Mobile is the Two Factor Authorization tool used by Virginia Tech to assist in securing access to sensitive University resources. In order to log into nearly all Virginia Tech Resources you will need your PID, password, and a third part from Duo Mobile (either a code, a phone call, or a link on your phone).
Below are links to various topics pertaining to Duo Mobile at Virginia Tech:
How to Authenticate using the various Duo Mobile Methods
Printing Backup Codes for when you do not have your device
Lost, Broken, or Unavailable Duo Mobile Device
Comprehensive List of all Duo Mobile Articles at Virginia Tech