1. A computer-implemented method comprising: receiving, by a computing system, a set of accounts associated with a specified time frame; analyzing, by the computing system, for each account in the set, one or more features and one or more feature combinations; determining, by the computing system, for each account in the set, feature metrics for the one or more features and the one or more feature combinations; acquiring, by the computing system, threshold values for the feature metrics; implementing, by the computing system, at least one rule for dynamically identifying accounts as being illegitimate, the at least one rule being based on at least some of the feature metrics and at least some of the threshold values; receiving, by the computing system, an unidentified account absent from the set of accounts; determining, by the computing system, that the unidentified account is associated with the one or more features and the one or more feature combinations; calculating, by the computing system, based at least in part on the feature metrics determined for each account in the set, one or more assessment metrics; and identifying, by the computing system, the unidentified account as being illegitimate, based on the at least one rule, when the one or more assessment metrics satisfy the at least some of the threshold values.