Physical layer security (PLS) provides an additional protection layer to the conventional encryption in the presence of an active eavesdropper (Eve). The detection of pilot contamination attack (PCA) on legitimate nodes by the active Eve is vital in order to mitigate the effect of the attack. In this work, we propose a novel PCA detector for the nodes, which intend to establish secure communication in time division duplex (TDD) mode over a frequency selective channel. We devise binary hypothesis from the decision directed channel estimate for PCA detection by exploiting observations of pilot sequence and random data in pilot and data phases, respectively. We also provide performance analysis of the proposed method. The comparison of simulation results and analysis demonstrates the accuracy of the analysis. The proposed detector has low probability of detection error as compared to the existing high complexity sub-space based PCA detector.