What is a host file and why do i need it?

A custom HOSTS file is another tool to protect your computer from malicious programs. When used correctly, it will keep you away from dangerous sites.

First, the HOSTS file contains IP (Internet Protocol) numbers associated with Web sites. Each Web site is identified by an IP number. For example, mine is 66.210.246.140. This number is the site's address.

IP numbers are difficult to remember. So Web sites use a name instead. Mine is www.komando.com. However, when the name is entered in a browser, it has to be converted to an IP number. The DNS (Domain Name System) associates the name with the site’s IP number.

When you enter a name in your browser, it first goes to your HOSTS file to find the IP number. That file is normally empty, or nearly so. Not finding the number there, it goes to a domain name server. It continues to query servers until the number is found, or it establishes that there is no number.

The HOSTS file can be manipulated to block malicious sites or ad servers. To do this, you list the name of the Web site you want to block. With it is listed the IP number 127.0.0.1. That is the number of your computer. Doing this has the effect of short-circuiting the request. The request just dies.

This actually can make your computer faster. When you open a Web site, the files that you want to see are downloaded from that site. But other files, usually for advertising, have to be opened from other computers. When those requests die in your computer, the page opens, minus the ads.

The HOSTS file also protects you from spyware on your computer. These programs use the browser to report your surfing habits back to a computer on the Internet. Requests to go to the Internet computers will be blocked by a good HOSTS file.

So a custom HOSTS file has an important security role.

It is true that a large HOSTS file can slow Web surfing in Windows XP and 2000. Earlier versions of Windows are unaffected. This can be remedied by turning off your DNS Client.

The DNS Client stores a list of IP numbers for Web sites you’ve visited. The computer searches the stored list before contacting the DNS server. Your computer is slow because it’s searching through this cache AND the HOSTS file. The HOSTS file is necessary. The cache is not.

To change this, click Start>>Run. Enter “services.msc” (minus quotes) in the box. Right-click DNS Client and select Properties. Click the down arrow beside “Startup type” and select Manual. Click Apply. Click OK and restart the computer. This keeps the DNS Client from loading at startup.

If you don't have a custom HOSTS file, you can download a free one. I use one maintained by Mike Burgess:
http://www.mvps.org/winhelp2002/hosts.htm

A HOSTS file complements your anti-virus and anti-spyware software. It does not replace them. If you need anti-virus and anti-spyware programs, you'll find free ones and free firewalls on the same page. Protecting yourself requires a mix of programs.
http://www.komando.com/bestshareware.asp
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A custom HOSTS file is a crucial defense against spyware and hijacking.
When a malicious program on your computer, such as spyware, attempts to
contact a computer on the Internet, it makes its request through the
browser, like Internet Explorer or Firefox.

In attempting to fulfill that request, it goes first to the HOSTS file
to try to find the IP number--the actual Web address. If it doesn't
find it there, it checks domain name servers on the Internet.

So, the spyware can be thwarted in the HOSTS file.

The HOSTS file I use has thousands of entries. Some are really
malicious sites. Others are just advertising sites. And some may be
sites you want to open.

So, let's say the file is blocking access to www.somewebsite.com. In
the HOSTS file, you'll find a listing that looks like this:

127.0.0.1 www.somewebsite.com

That IP number is your machine's address. When you try to go to
www.somewebsite.com, you're actually being redirected to your own
computer. Your request dies. So you have to tell the HOSTS file to skip
this entry. To do that, "comment out" the www.somewebsite.com line:

#127.0.0.1 www.somewebsite.com

The pound mark tells the HOSTS file not to read that line. Stick it in
there, click File>>Save and close the file. Be sure you've gotten all
the somewebsite lines. There could be more than one.

You also could delete the somewebsite line. But I prefer to comment it
out. You never know; you might want to reinstate it in the future.
You'll have to comment it out (or delete it, if you prefer) each time
you update the HOSTS file.