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Knowledge_factor part of MFA and includes all things users must know in order to log in to gain access to a system. This includes Usernames, IDs (i.e., Passport or Driver's license numbers), passwords, and personal identification numbers (PINs), answers to security questions(i.e., your favorite sport), or information derived from Personal Identifiable Information (PII) (i.e., mother's maiden name, oldest child's middle name). See CyberSecurity Culture (CSC)
Source: https://searchsecurity.techtarget.com/definition/multifactor-authentication-MFA