Hardware Security is the key aspect of the integrated circuit’s life cycle; Any malicious modification in the system design at the foundry is a significant concern for hardware threats, known as a Hardware Trojan attack. These Trojans are very difficult to detect in the real world, even during manufacturing and testing. In this article, the impact of Hardware Trojan on the performance of the cache memory is presented. Insertion of Trojan demonstrated in the cache replacement policy, which replaces the original cache replacement (least recently used, first in first out, and least frequently used) policies with another replacement policy (most recently used). The performance was analyzed in the gem5 simulator after inserting a Trojan. It was clearly evident that Trojan insertion degrades cache performance and affects overall processor performance. It is observed that the impact on the Trojan was a savior on LFU compared to other cache replacement policies, since LFU persists in its counter-based memory.