When you browse the Internet the Windows Hosts file controls the browsing process. As a result, since the file is that important, it is susceptible to malware infections. When this file is damaged, it directly affects your ability to open various websites, and you can also be forcefully redirected to certain infected webpages.
In order to restore the Hosts file, you must first find it in this location: C:\Windows\System32\drivers\etc. Sometimes you might not find the file, and it happens because the operating system files are hidden by default. Then, if you use Windows XP, you need to go the Folder Options Control Panel, and uncheck the "Hide Protected Operating System files" option. The file that you need to find is titled "hosts".
Take note, that modifying the hosts file is a serious business, so if you are not sure of what you are doing, you should better ask for help from a computer expert. In order to restore the Hosts file to its default configuration, try using Microsoft’s tool called "Fix it".
Sometimes you will not be allowed to modify the Hosts file without the administrative access. You can get the access in Windows Vista or Windows 7 by going to Start --> All Programs --> Accessories. Then right-click the Notepad icon and choose to "Run as administrator". When Notepad loads, select File --> Open, and navigate to the Hosts file’s location to open it and modify it as you want.
