Systems and methods are disclosed for providing distributed denial-of-service (DDoS) mitigation service. The systems and methods may receive a request to access a web server from a user host, generate an integrated user challenge page including a user challenge test and a web page image of the web server, and transmits the integrated user challenge page to the user host. The systems and methods may further receive an answer to the user challenge test from the user host, determine whether the answer to the user challenge test is correct or not. When the answer to the user challenge test is correct, the systems and methods may establish a connection between the user host and the web server.