User-Agent is the header sent by web browsers to provide web browser software information to web servers. This header must be filtered using the RequestFilter interface since the header is sent by the browser as part of each request. To accomplish this, a filter can implement the RequestFilter interface and in this implementation provide a filter() method that removes the User-Agent header from each Request object. A similar solution can be used to remove Referer, which is the other privacy-related header discussed in Chapter 3 that can be sent by the browser.