A little about host names and
IP addresses before we get into the fun stuff. Host names are the www
URL names that you see everyday. IP addresses are the same, but is in
the form of numbers. When typing in a www address, the computer translates
it into an IP address before looking it up. www.yahoo.com is much easier
for people to remember and use than, lets say, 204.71.200.67.
When translating, the computer takes a series of steps, but the most important
one is the use of the Hosts file on your computer. The Hosts file tells
your computer what the name is in numbers so the computer can go find
it. If the IP address is found in your Hosts file, the computer will stop
looking and go to that site, but if it is not it will ask a DNS computer
(domain name server) for the information. Since the search ends once a
match is found, that provides us with a mechanism to block sites we have
no interest in. You may block sites that serve advertisements, sites that
serve objectionable content, or any other site that you choose to block.
Computers have a host address of their own - it is known as the "localhost"
address, with an IP address of 127.0.0.1 which it uses to refer to itself.
If you associate another computer's host name with your localhost IP address,
you have effectively blocked that host since all attempts to access it
will lead back to you. That is how we will block sites using the Hosts
file. We will tell our computer that the IP address of the site we want
to block is our own address. That way, our computer will not ever leave
and go looking for the site we are blocking - which keeps that site from
appearing because the computer thinks it has found the site and displayed
it already.
Many web sites have links to other servers for the retrieval of advertisements.
In the case of those web servers, the browser will quickly fail to locate
the requested data (scripts, images, etc.) from the advertising server
because we told our computer to look for the information on itself - of
course it won't find any of it and will quit looking for it - and will
continue loading the pertinent portions of the page you want to see. This
will keep your computer from even talking to the ad servers, and thus
you won't see the ads, they can't put cookies on your hard drive, and
you can't be profiled by them.