Noun
identity fraud; masquerading (as somebody else)
Usually written using kana alone
人のパスワードを乱用する「なりすまし」行為が問題になっている。Now that people can steal passwords, illegal impersonation is becoming a serious problem. spoofing; forgery (e.g. of email)
ComputingUsually written using kana alone
Also written 成り済まし【なりすまし】