This paper focuses on cyber-security issues of networked control systems in closed-loop forms from the perspective of quantized sampled-data systems. As sampling can introduce non-minimum phase zeros in discretized systems, we consider zero dynamics attacks, which is a class of false data injection attacks. Quantization of control inputs disables such attacks to be made exactly, resulting in certain errors in the system output. Specifically, we characterize a trade-off relation between attack performance and stealthiness, and then show that the attacker can reduce the output error with a modified approach by considering the quantization error of the attack signal. We provide a numerical example to demonstrate the effectiveness of the proposed approaches.