Previous results on blind multiuser detection apply in situations where the signal parameters of the users of interest are known, and those of the interferers; are unknown. In this paper, we consider the new paradigm of an N-user system, in which K users are active, and the problem is to detect G users of interest out of those K active users when the signal parameters (codes, amplitudes) of the G users of interest are known, as are the codes of all N users. What is not known at the receiver, however, is K - G, the number of active interferers, and the identity of these interferers. A solution to such a problem could be to ignore the knowledge of the remaining N - G codes, and apply known blind multiuser detectors based on stochastic approximation or subspace tracking techniques. However, it is shown here that the additional knowledge of those codes can be used to obtain an interference-identification-based blind multiuser receiver that has much faster convergence properties. We illustrate the underlying principle in the context of blind group detection in synchronous direct-sequence/code-division multiple-access (DS/CDMA) systems operating in channels that exhibit frequency-selective fading.