The hosts file represents the list of compliance of domain names and IP addresses provided in a simple text format. In case of the Windows operating system it represents the file with the name hosts (but without expansion) which is usually located in the etc folder.
Hosts file
The hosts file is necessary that the operating system could compare domain names to certain IP addresses. It represents the simple text file and in case of the Windows operating system is located in the system32\drivers\etc\folder. Sometimes its location is redefined through the system registry. In case of the Mac OS operating system the hosts file usually locates at address/private/etc.
If to open the hosts file by means of a notepad, it is possible to see in it the following record:
127.0.0.1 localhost
It means that your computer has IP address 127.0.0.1. This IP address registers for any home computer - such reception is called "an internal loop". It allows programs servers to work correctly, being installed on the same computer, as client programs.
Change of the hosts file
Changing the hosts file, it is possible to block access to the websites or to redirect the user to the IP addresses, other than those which are stated in the DNS system.
For example, such record will back "loop back" all requests sent for the domain microsoft.com on the computer:
127.0.0.1 microsoft.com
And the following record will redirect the user who gathered the address "google.com" in an address bar of the browser, on servers of Yandex search engine (IP 77.88.21.11 belongs to Yandex):
77.88.21.11 google.com
Hosts file and swindlers
Also malefactors sometimes use similar redirection. They infect the computer with a virus which substitutes the "native" hosts file on that which is created by the hacker. In such file usually the addresses of all popular searchers, mail services and social networks are redefined on IP of the websites which are managed by the malefactor. The user does not notice a difference between the real and counterfeit website and tells hackers the personal data, passwords, etc. If you found on the computer in the hosts file suspicious records (domains of search engines, social services, e-mail servers, instant messaging systems, etc.) - immediately delete these lines.
To protect users from swindlers of this sort, many software developers release programs which block the hosts file from changes or in due time inform the user on these changes. Many free firewalls have such function, for example.