This is a good definition in layman's terms:


http://accs-net.com/hosts/what_is_hosts.html

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Okay, why do I need to know this? Because there are certain applications that maliciously block sites by putting entries in the Hosts file. The way this works is that each site has an IP address, which is a series of four sets of numbers, separated by periods. This is the "phone number" mentioned above. One particular IP (127.0.0.1) corresponds to the local computer. So lets say that the entry in the hosts file is changed and this entry is added:

www.yahoo.com 127.0.0.1

When you try to go to www.yahoo.com, the computer will look in the host file and see that IP. It will then say, "Oh, well this is my own local IP, so www.yahoo.com must exist on my own system." Since in reality, it DOESN'T exist on the local system, it will time out when looking for yahoo.com and will never show the site. I'm using yahoo.com as an example, but it can be any site.

The good news is that you can fix this. First, do a search for "hosts", without the quotation marks. Several may be found, however disregard any that have an extension. Usually the hosts file will either be in the System folder or in the I386 folder.

Double click it to open it, selecting NotePad as the program to open it with. Find the entry that is incorrect, in the case of the example above, www.yahoo.com. Erase the whole entry:

www.yahoo.com 127.0.0.1

Then go to File and Save. That is all there is to it.