We propose an artificial noise (AN) injection strategy for securing communication over finite-input intersymbol interference (ISI) channels. The technique relies on injection of colored noise whose power spectral density has the least match with the spectrum of the main channel in a certain sense. By evaluation of an achievable secrecy rate, we demonstrate that the proposed AN injection based solution results in a considerable improvement over the existing approaches, especially when the eavesdropper works at high signal-to-noise ratios (SNRs).Index Terms-Physical layer security, finite-state wiretap channel, artificial noise, inter-symbol interference.