Host Files - What are they and what do they do
A host file acts rather like a telephone directory for the internet. Each web site address has its own IP (Internet Protocol) address. In order to reach a web address your computer needs to change the address you type into the addres bar - known as the URL (Uniform Resource Locator) - into the IP for that particular site. Imagine that you are trying to ring a certain Mr Smith - first you need to find the number that you can contact him on before you can telephone him. Your computer works in a similar way, when you type in a web address, it first checks your host file which is located on your computer to see if the IP address for that site is stored there, then, if not, then the address is resolved by your ISP's DNS Server (Domain Name Server.) Imagine it this way - you first look for Mr Smith's address in your personal address book, then, if you do not have you look it up in a telephone directory.
Let's take this address, type the following into your browser: www.bbc.co.uk - This address takes us to the BBC's website. The IP address for this particular page is 212.58.224.89 you can test this yourself by going back to your homepage then typing the IP as you see it into your browser. No matter if you typed in the full address or the IP address you end up at the same location.
A host file works by converting the web address on the right hand side to the IP address on the left, the above in a host file would typically look like the following.
212.58.224.89 www.bbc.co.uk
Having a host file on your computer can slightly speed things up as it means your computer does not have to look up the address in the DNS server from your ISP (Internet Service Provider). With a host file you can map out addresses if you know the IP for the site.
But.... Hold on.... the best way in which the host file can be used is for blocking sites. Think of things like this, you want to ring Mr Smith but you enter the wrong number, instead of reaching your contact you reach the wrong person. This can also apply to a host file. By using the IP address of 127.0.0.1 we can redirect websites back to your computer instead of the website, the IP address of 127.0.0.1 is knows as a loopback address. This is how it would typically look in a host file.
127.0.0.1 www.badwebsite.co.uk
This would then prevent any access to www.badwebsite.co.uk by redirecting you to your loopback address, this way you can block out known adservers, banners, and data miners
This is all good and fine.. but wait, let's see the other side of the coin too.... what if something changed your hostfile. Certain Malware has the ability to do this, instead of reaching an anti virus web site such as for example norton, malware can write and add entries to the host file so it redirects you back to your computer. Harmless as this may seem, just think if you are infected and you wanted to run a scan or you wanted to download a removal tool. The hostfile would prevent you from doing so.
How to find your hostfile...
You can find your hostile in the locations listed below
- Windows Vista: - C:\WINDOWS\SYSTEM32\DRIVERS\ETC
- Windows XP: - C:\WINDOWS\SYSTEM32\DRIVERS\ETC
- Windows 2K: - C:\WINNT\SYSTEM32\DRIVERS\ETC
- Win 98/ME: - C:\WINDOWS
Managing the hostfile
The best way to manage your host file is by using a dedicated host file manager, a good one to use is hostexpert by Funkytoad. This handy utility will allow you to write, append, and also lock your host file so malware is unable to write and edit entries to it. Also, if you have an infected host file then Hostexpert also allows you to reset the hostfile back to the default settings. As well as managers you can also download preset host files, probably the most popular host file is the MVPS Hostfile This hostfile is also available in text format too and can be located here
I hope this article comes accross to you as I planned it to! If you are unclear on any part of it feel free to contact me via the contact page on this site and I will reply to you as soon as I have the available time to do so