A captive portal system includes a login database, a web server, and a name server. The name server receives a DNS request from a user device, queries the login database to determine whether the user device is logged in, and responds to the DNS request with the IP address of the web server as a resolved IP address of the specified domain name when the user device is not logged in. The web server accepts a connection request from the user device to the IP address of the web server, receives an HTTP request specifying a non-local target URL from the user device, queries the login database to determine whether the user device is logged in according to the source address of the user device, and acts as a transparent proxy between the user device and the non-local target URL when the user device is logged in.