In this paper we present a security checking module meant to be connected between the microprocessor and the instruction memory in order to monitor the fetching activity with the aim of detecting the activation of HTHs. In particular, we aim at detecting those HTHs that alter the expected execution flow by launching a malicious program. We integrated the proposed security checking module within a case study system based on a RISC-V microprocessor implemented on an FPGA and running a set of software benchmarks. This experiment demonstrated that our proposal is able to detect 100% of possible HTHs activations with no false alarms. We measured a LUT overhead of 0.5% and a FF overhead of 0.3%, with a 2.36% power consumption increase and no working frequency reduction.