Provided are an apparatus and method for extracting user information using a client-based script in which user information including the internet protocol (IP) addresses of an attacking host and an anonymous proxy server used by the attacking host can be collected using a client-based script that can be automatically executed in the web browser of the attacking host. According to the apparatus and the method, it is possible to detect the location of an attacking host without alerting the attacking host by using a script that can be automatically executed in a web browser of the attacking host without any program installation. In addition, according to the apparatus and the method, it is possible to collect the IP addresses of an attacking host and an anonymous proxy server, if any, used by the attacking host by directly connecting the attacking host and a monitoring server.