Final answer:
The correct method to identify when an unauthorized access has occurred is C. Previous Logon Notification, as it notifies users of the date and time of the last account access.
Step-by-step explanation:
Identifying Unauthorized Access
To determine when unauthorized access has occurred, certain security measures can be implemented. While Two-factor Authentication (2FA) adds an extra layer of security by requiring a second form of identification, it doesn't directly notify users of unauthorized attempts after they happen.
Session Termination refers to ending a user session, perhaps after a period of inactivity or after a number of failed login attempts, to prevent unauthorized access, but again, it does not notify of past intrusions. Session Lock prevents unauthorized access during a user's active session, by locking the session after a user steps away, but it does not alert to prior unauthorized attempts.
Previous Logon Notification is the method that informs a user of the last date and time their account was accessed, which can alert a user to any potentially unauthorized access if the logon was not initiated by them. Thus, the correct option that could identify when an unauthorized access has occurred is C. Previous Logon Notification.