User authentication system

A non-transitory computer readable medium having machine-executable instructions with which a computer having a storage and a hardware processor connected via a network to a user terminal device operate as:

• login receiving means, which receives an account login request from the user terminal device along with account identification information and authentication information;
• authentication processing means, which determines whether or not the combination of the account identification information and the authentication information received by the login receiving means matches a pre-stored combination of predetermined account identification information and authentication information, and, in the event of a match, authenticates said user terminal device;
• fraud determination means, which detects fraud in the login request from the user terminal device based on the access history of the user terminal device;
• and
• response control means, which
• allows the user of the said user terminal device to log in to the predetermined account if the fraud determination means does not detect fraud in the login request from the user terminal device and the authentication processing means has authenticated the user terminal device,
• allows the user of said user terminal device to log in to a dummy account in accordance with predetermined criteria if the fraud determination means detects fraud in the login request from the user terminal device and the authentication processing means was unable to authenticate the user terminal device, and
• does not allow said user terminal device to log in to the predetermined account or the dummy account and delivers an error notification to said user terminal device if the fraud determination means detects fraud in the login request from the user terminal device and the authentication processing means has authenticated the user terminal device.