The Hosts file
contains the mappings of IP addresses to host names. The Hosts file is
loaded into memory (cache) at startup, then Windows checks the Hosts file
before it queries any DNS servers. This action enables Windows to
override web addresses in the DNS servers your computer is using to look
up web addresses. Doing this prevents access to the listed sites by
redirecting any connection attempts back to the local machine or localhost.
The HOSTS file is also able to block other applications from connecting to
the Internet, providing the entry exists in the Hosts file. You can
use a HOSTS file to block ads, banners, 3rd party Cookies, 3rd party page
counters, web bugs, and even most hijackers. This is accomplished by
blocking the connection(s) that these programs use.
The Hosts file is located
Windows XP =
Windows 2K = C:\WINNT\SYSTEM32\DRIVERS\ETC
Win 98/ME = C:\WINDOWS
For more information on the Hosts File
There's No Place Like 127.0.0.1
What is the Hosts file?