Dns Poisoning Is it really possible ?

[longtimeago 0]

I came across a kind of attack by name DNS poisoning , and i was learning about the same , to put it in simple words DNS poisoning is one where the Domain Name Server of an organization is being poisoned. As most of us are aware when we keen in a website ( URL ) in the web browser what actually takes place is the conversion of domain name to IP address. So this takes place at sevral place , but primarily this takes place in the Local Domain Name Server of the network from which the user is browsing.So i also understand what is inside this server , just 2 collums , Domain name and the corresponding IP address. Now as the topic says Domain Name Server Poisoning, if someone can hack into this domain name server and can change the IP address of a website to his/her server then he can accomplish the task of harvesting sensitive information, Now my question is , is it really possible ? I do understand that if you hack inside the server then one can accomplish the task of poisoning the Domain Name Server.But please tell me is it really possible to hack the domain name server ?? If so what are the ways in which it can be done ?? and what are the ways to prevent it .