The use of a captive portal is designed primarily for network access control, often used in public Wi-Fi networks to present a webpage for user authentication. However, it does not inherently secure data transmissions. Without the help of strong encryption protocols like WPA2/WPA3, data sent over a public Wi-Fi network can be intercepted and is not considered secure. A captive portal prevents unauthorized access to the Wi-Fi network but does not encrypt data in transit between the client device and the access point, leaving it vulnerable to interception and eavesdropping.