A method, and associated system, for security processing of a request for a resource in a network security system. The request for the resource is received from a client device. A duplicate of the received request is created. The received request and its duplicate are forwarded to a first proxy server and a second proxy server, respectively. A first output including the received request, and a second output including the duplicate of the received request, are received from first proxy server and the second proxy server, respectively. A determination is made of whether the first output and the second output differ; if not the received request or the duplicate of the received request is transmitted to a web server for satisfying the request; if so a first alarm is generated and transmission to the web server of the received request and the duplicate of the received request is blocked.