The “Hosts” file has existed in most, if not all, operating systems since the beginning days of the Internet — back when there was no distributed host name database or “Domain Name Server” (DNS). Each network node maintained its own map of the network nodes as needed and assigned them names that users could (hopefully) remember. This worked when the internet (or ARPANET as it was known back then) was fairly small… but not any more. Most all the OS’s in use today still have the HOSTS file. In most Windows boxes, it normally has only one entry (127.0.0.1 localhost).
The purpose of the “Hosts” files is really simple — it maps IP addresses to host names. Windows (and other OS’s) check this file BEFORE querying any DNS servers. This allows it to not only OVERRIDE addresses in the DNS, but to BLOCK addresses, too.
Please check out the site “Blocking Unwanted Parasites with a Hosts File.” This site provides a new Hosts file monthly that is tailored to block ads, banners, 3rd party cookies and more. The MVPS HOSTS file now includes most major parasites, hijackers and unwanted Adware/Spyware programs. To download, look for the yellow file folder & right-click on “hosts.zip” & select Save Target As. The file was last updated on Sept 22, 2010. The site provides all the necessary info you need for copying the Hosts file to the necessary location on your system.
I’ve been using the MVPS HOSTS file on all my systems for over three years and cannot imagine accessing the Internet without it. I STRONGLY recommend using it!