The hosts file could be described as an address book. While the normal user is accustomed to access other computers on the internet using names (for example security.kolla.de), every computer is accessed by a numeric address at a lower level. You may already have seen this numeric addresses; they look like 127.0.0.1 for example.

Every time you try to access another computer by using his name, your computer looks up his address in an address book. First it looks into a local address book (the hosts file), and only if it cannot find the address there it looks in a very big address book in the internet.

So, if you want to block an internet web site, you could simply redirect this sites name to a place where nothing will be delivered from. Such a place would be your computer for example. The address I already mentioned, 127.0.0.1 is an address that will always point to the local - your - computer. By adding an entry to the hosts file (your local address book) that redirects an ad site to your machine, you would trick your internet browser to think that ad site would be on your machine, and as your machine does not deliver ads, it would not get the ad and it will not be displayed.

Another way of using the hosts file is if you want to access computers that are not listed in any address book yet. For example if you have a local network, you would not list your local computers in any internet address book, if only because that would be very expensive. So you could just enter them into the local address book (your hosts file).

Spybot-S&D can add a prepared list of web sites known for bad behaviour (installing spyware or tracking users, for example) to your hosts file. If you want to do this, we recommend you also read the FAQ about cures for possible slow-downs on Windows NT based systems (Windows NT, 2000, XP and Vista). And if you should notice you cannot visit a site that worked before, you should check the Hosts file section to see if that site is on the block list.