The broad landscape of new applications requires minimal hardware resources without any sacrifice in Quality-of-Results. Approximate Computing (AC) has emerged to meet the demands of data-rich applications. Although AC applies techniques to improve the energy efficiency of error-tolerant applications at the cost of computational accuracy, new challenges in security threats of AC should be simultaneously addressed. In this paper, we introduce the security vulnerability of the concurrent AC synthesis. We analyze the threat landscape and provide a broader view of the attack and defense strategy. As a case study, we utilize AC synthesis technique to perform malicious modifications in the synthesized approximate netlist. Similarly, we provide a scalable defense framework for trustworthy AC synthesis.