How does web filtering software hook into outbound browser requests without browser configuration?

Question

I would like to duplicate the functionality of some web filtering software, however I don't want the user to have to configure their browser. Some other products on the market do this without any apparent configuration in the browser settings.

The user would be installing this for themselves, so air-tight filter security is not a priority. But ease of installation and the ability to apply to an arbitrary browser would be important.

Since the vision is standalone desktop software, inserting a filter on another upstream machine is not really an option.

Answer 1

Install your program as a proxy for all HTTP traffic.

Answer 2

You will need software that runs on a network node that all internet flows through, and it will have to intercept HTTP requests and redirect them accordingly.

Some routers have this sort of capability, it can also be accomplished with linux routers using iptables and a squid proxy.

Answer 3

Windows Filtering Platform

Windows Filtering Platform (WFP) is a set of API and system services that provide a platform for creating network filtering applications. The WFP API allows developers to write code that interacts with the packet processing that takes place at several layers in the networking stack of the operating system. Network data can be filtered and also modified before it reaches its destination.

http://msdn.microsoft.com/en-us/library/aa366510%28VS.85%29.aspx