Um, good question. I've used this before, many times, and it does work. But I've never done it the way cyber has explained it. What I do is first get the IP of the site. You can do this by clicking start > run > and type in
cmd > then type in
ping www.website.com. Once you have your IP, go into your hosts file, you should see something like this:
127.0.0.1 localhost
paste the IP where the ip goes, and type in the full url under local host. So it should look like this:
127.0.0.1 localhost
111.11.111.111
www.website.com
*Note that if the IP of the site changes, (if they change servers, etc) then the IP also changes, and it needs to be changed in your hosts, or removed completely.
Also, if you have MS antispyware, or anything similar, it might warn you that your hosts is being changed, just allow it.
Now to block and add, type in 127.0.0.1 right before the url so it should look like this.
127.0.0.1 localhost
111.11.111.111
http://www.website.com
127.0.0.1
http://www.ads.com
But first you need the URL of the ad, to do that, you can either right click on it with firefox, and go to properties. With IE, do the same.
You can even block whole websites with this. All you do is just put in a false IP, or an IP that doesn't exist, (random numbers that resemble an IP address) and then put in the URL of the site, but make sure you put in the
HTTP://, and then another line without HTTP://
Every enter, whether your blocking an ad, a site, or making a site load faster, needs a new enter. Like this:
127.0.0.1 localhost
111.11.111.111
http://www.website.com
127.0.0.1
http://www.ads.com
ip site
ip2 site.com
ip3
www.site.com
etc..