Blocking Unwanted Parasites (ads) using your Hosts File
What your hosts file does ...
The Hosts file contains the mappings of IP addresses to host names. This file is loaded into memory (cache) at startup, then Windows checks the Hosts file before it queries any DNS servers, which enables it to override addresses in the DNS. This prevents access to the listed sites by redirecting any connection attempts back to the local (your) machine. Another feature of the HOSTS file is its ability to block other applications from connecting to the Internet, providing the entry exists.
You can also download a hosts file with lots of ad blocking already added @ http://everythingisnt.com
Or you can manually type your own by adding entry's like this:
127.0.0.1 ad.preferences.com
Then save the hosts file with the changes you made