Mobile network-based multi-factor authentication

A multi-factor authentication method using a mobile device as a token to protect against fraudulent on-line purchases, the method comprising:

• receiving at an authentication server, a request for authorization of an on-line transaction from an application server associated with a restricted-access account, wherein the on-line transaction is initiated by the mobile device using the restricted-access account, the request including a first user name associated with the restricted-access account, an IP address of the mobile device that initiated the on-line transaction, and an account number identifying a payment account for the on-line transaction;
• verifying at the authentication server, that the first user name matches a second user name currently registered as a user name for a network identification (ID) of the mobile device, wherein the network ID of the mobile device is determined from a link between the network ID of the mobile device and the restricted-access account;
• verifying at the authentication server, that an initiation location of the on-line transaction matches a current location of the mobile device, wherein the initiation location of the on-line transaction is determined from the IP address included in the request;
• verifying at the authentication server, that a third user name registered as a user name for the payment account matches the first user name;
• determining at the authentication server, an authorization score for the on-line transaction based on verifying that the first user name matches the second user name, verifying that the initiation location of the on-line transaction matches the current location of the mobile device, and verifying that the third user name matches the first user name;
• and
• transmitting by the authentication server, the authorization score to the application server, which determines whether or not to allow the on-line transaction to proceed.