The main disadvantage of using wireless networks compared to wired connections is security. Wireless networks are more susceptible to unauthorized access and eavesdropping due to the data being transmitted over the air. While encryption methods can mitigate risks, they are not foolproof. Additionally, wireless signals can be disrupted by physical obstacles, resulting in reduced bandwidth and increased latency. These factors can impact overall network performance and reliability, making wired connections preferable in high-security environments.