Hello, I find this information in a website.
You can see whether it can help you:
When you surf to a site, Windows automatically checks to see if the address is located in the Hosts file. The number 127.0.0.1 is the "loop back" IP address of your own computer, so Windows skips the link to the site (media.fastclick.net) and moves on. The ad server can't open its window, so it can't load any programs, spyware, or cookie files either.
You can open the Hosts file in Notepad and edit the entries so the sites you want to avoid are blocked. In Windows XP, the file is located in the C:\Windows\System32\Drivers\Etc folder. You can learn much more about the Hosts file at this page: http://www.mvps.org/winhelp2002/hosts.htm
In fact, this page also has a downloadable Hosts file you can use just by copying it into the Etc folder. Or you can view the file to see what evil parasitic sites you want to avoid. The downloadable Hosts file is 318K and the page has a note that says Hosts files that are larger than about 135K can actually slow down your computer.
As a compromise, I just copied out the lines for the ad networks I knew about from the downloaded file into my Hosts file. Over time, I may find more annoying sites, and I'll just add those entries into the file. Having the download as a reference is really handy, since it has comments that explain what some of the bad sites are up to.
The source:http://www.logicaltips.com/LPMArticle.asp?ID=506 Answered Apr, 12 2011