This file named 'hosts' will intercept and block most known ad and malware access
that your computer may attempt.

To install, simply copy the hosts file to the correct location on your computer.
There normally will already be a hosts file there. You can safely overwrite it.

Where to put the hosts file:

Windows 9x, Me:	c:\windows
Windows 2000:	c:\winnt\system32\drivers\etc
Windows XP:	c:\windows\system32\drivers\etc
Linux:		/etc
MacOS:		? (find where the existing one is located)

NOTE: 

If you are running the DNS Client service on Windows (most are)
you should either stop the DNS Client service, restart the service, 
do the command ipconfig /flushdns, or restart Windows. Windows may be 
very sluggish until this is done.

On Windows 2000, XP, Vista, Windows7 I recommend disabling the DNS Client. 
It seems to cause more trouble than its miniscule benefits are worth.