u can put it in ur host files so windows looks up the ip addy of adfarm there first before going to a dns server to find the ip and instead of putting the correct ip of adfarm in put ur local address in. that way windows basically tries to connect to itself when it wants to connect with adfarm. do it like this. open ur host files with note pad. it is located at windows/system32/drivers/etc. type 127.0.0.1 at the beginning of a new line(that is ur local address) then put a space and then www.adfarm.com
after that and all should b well. make sure to save it without a file extension and not a .txt ext either after editing with notepad. be aware if that server is hosting more than ads like actually parts of the website it will block that also. if that confuses u windows has a sample hosts file in that one that u will edit showing how to do it.
hope that helps
heres some more stuff on this,
here is what the host file is in more depth. http://www.accs-net.com/hosts/what_is_hosts.html
and here is a premade hosts list that u can just copy and paste in overwriting the original to block hundreds of ad servers
open it with notepad after u extract it to see all the different ad servers blocked with it.