How Can DNS Poisoning Be Explained?

The job of a DNS or Domain Name Service is to convert the human readable addresses entered into the address bar of a browser into machine readable IP addresses.  

For example when you type the URL (www.hotmail.com into the address bar the first thing that occurs is the nearest DNS server is contacted and the IP address of hotmail domain is retrieved.  Based on this IP address the website is opened.

So a DNS is a huge database that stores IP addresses of different domains.  These are cached and updated on a regular basis.

DNS poisoning is also called DNS cache poisoning, and refers to the corruption of DNS tables and caches so that a domain name points to a malicious IP address.  Once the user is re-directed to the malicious IP address his/her computer can be infected with worms, viruses, spy ware etc.

Cache poisoning is mostly done through spam emails, or through web-links and banners that attracts users to click on them.  A simple click causes the user to be re-directed to a DNS poisoned server.  

There is also another form of DNS poisoning where valid email addresses are flooded with information.