Learn in the textbookClassifying Threats — Human Wrongdoing and Accidents
DefinitionImpersonation (なりすまし) means posing as another person or a legitimate organization and acting as them to obtain information or carry out improper operations.
ExplanationBesides logging in with a stolen ID and password, it can also mean faking an identity by phone or email to deceive someone. The basic countermeasure is user authentication, which checks whether the other party really is who they claim to be.
AnalogyIt is like wearing someone else's name badge to slip into a meeting and speak as that person.
Memory hookThe Japanese verb 成り済ます means to become someone completely.