Knowledgebase: SpywareBlaster > Tools
What is a Hosts file?
Posted by BrightFort Support, Last modified by BrightFort Support on 25 February 2008 03:50 AM

Some Background

Every web address you enter into your web browser (ex. ""), has a corresponding IP address (eg. ""). The IP address is much like your physical address - it describes where a server resides (so your computer can connect to it). But, obviously, a series of numbers are less memorable than a more human-readable format of letters/words.

Your web browser translates the web address you enter into its corresponding IP address by connecting to a DNS server - which, similar to a phone/address book, provides a listing of all web addresses and their corresponding IP addresses.

Thus, you can remember (and enter) the more memorable web address (, and your browser can still find the website by looking up its IP address (

A Hosts File

A Hosts File on your computer acts like your own special phone book. Just like a DNS server, it lists a web address and its corresponding IP address.

But there are some important differences:

  1. If a web address is listed in the Hosts file on your computer, your browser uses that entry instead of querying a DNS server.

  2. There is no check on whether the IP address listed in the Hosts file is correct. It can be a local address (, which effectively blocks access to the site, or it can be the address of an old or malicious web server, which prevents you from accessing the actual web site.
So the Hosts file on your computer has the potential to be both good and bad.

  • If a web address and its associated IP address are listed in your Hosts file, your computer does not have to query a DNS server to find the IP address of the site. This can be slightly faster, depending on circumstances.

  • Some services provide Hosts files that block access to a number of bad sites, or advertising sites. They use the ability of the Hosts file to point a web address to an incorrect IP address (such as the local address, to prevent your computer from connecting to download ads or other potentially unwanted material.
  • If a web site has moved to a new IP address, an old entry in your Hosts file can render it inaccessible.

  • Some malicious programs use the features of the Hosts file to redirect legitimate sites (such as banking sites) to fake servers, which can put your personal information at risk, block access to legitimate resources, or expose your computer to more ads or exploits.

SpywareBlaster provides the ability to keep encrypted backup copies of your Hosts file. Should an unwanted program change your Hosts file maliciously, SpywareBlaster makes it easy to restore a good backup copy of your Hosts file - and restore proper access to web sites.

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