A Web filter is a program that can screen an incoming Web page to determine whether some or all of it should not be displayed to the user. The filter checks the origin or content of a Web page against a set of rules provided by company or person who has installed the Web filter. A Web filter allows an enterprise or individual user to block out pages from Web sites that are likely to include objectionable advertising, pornographic content, spyware, viruses, and other objectionable content. Vendors of Web filters claim that their products will reduce recreational Internet surfing among employees and secure networks from Web-based threats.
Some Web filter products also provide reporting so that the installer can see what kind of traffic is being filtered and who has requested it. Some products provide soft blocking (in which a warning page is sent to the user instead of the requested page while still allowing access to the page) and an override capability that allows an administrator to unlock a page.
While a Web filter can screen out a certain amount of malware, security experts advise other forms of protection as well, such as the installation of desktop and network antivirus software. A Web filter is often installed as part of a proxy server and firewall.
Also see content filtering.