LinuxWebLog.com

If you're looking to block online site ads and offensive Web content, you don't need to buy special software. Instead, you can use the HOSTS file built into Windows.

Few web sites host their own banner ads. Typically they sign up with ad servers that deliver content and track views and clicks. Thus you can block most web site ads by blocking a fairly limited number of ad servers. HOSTS files can block web ads by blocking access to these ad servers. Similarly, you can also block other sites serving objectionable content.

What Is the HOSTS File?

Unless a computer is configured to use a proxy server, the HOSTS file is the first place a browser looks for an IP address when you type in a URL such as www.permutations.com. Only if the domain name is not found in the HOSTS file does the browser then query the DNS server. It is this fact that makes the HOSTS file an effective means for blocking web site ads.

The HOSTS file is stored in different places depending on your operating system:

Windows 95/98/Me             c:\windows\hosts 
Windows NT/2000/XP Pro       c:\winnt\system32\drivers\etc\hosts
Windows XP Home              c:\windows\system32\drivers\etc\hosts

It's a text file you can open in Notepad. Comments at the top explain the simple syntax. Each line consists of an IP address, a domain name, and an optional comment placed after a pound sign. The one default entry in every HOSTS file looks like this:

127.0.0.1      localhost      # this is the IP address of your local computer

127.0.0.1 is a special IP address called the "loopback" because it refers to the local computer. The loopback address gives developers a way to test network software without being physically connected to a network. This prevents buggy network hardware or software from obscuring test results. The loopback address also can be used to prevent web ads from displaying.

To use the HOSTS file to block web ads, you add a list of hosts serving objectionable content (such as ad servers), and associate these domains with the loopback address -- your own computer. Then when you navigate to a site that contains banner ads, the browser looks on your own machine for the ads and never visits the ad server. Thus the ads are never displayed, and the ad server has no opportunity to put tracking cookies on your computer.

Compiling a list of ad servers for an ad-blocking HOSTS file would take a lot of time, but happily you don't have to do it. There are numerous ad-blocking HOSTS files available for download on the Internet. Mike Scallas distributes one that is updated each month.

Regular updates are necessary because new ad servers pop up all the time. If you see an ad while running an ad-blocking HOSTS file, it means one of two things: (1) the ad is hosted on the site's own server, or (2) it's new. To find out where the ad is coming from, right click on it and select Copy Shortcut. If the ad is hosted on the site, you can't block it with a HOSTS file because HOSTS files only can block entire sites. If it's a new ad server, paste the domain portion of this URL into your HOSTS file with a redirect to 127.0.0.1 and enjoy the extra speed that you get with your surfing without having to download the addition banner-ad images!!