DNS Poisoning - Is it effective?

What is DNS Poisoning?

This is a filtering method commonly used by ISPs to block access to a small list of blacklisted sites (in the thousands) such as ones containing images of child sexual abuse across their whole network. 

How Does DNS Poisoning Work?

It works by ISPs changing the DNS records of the blocked web sites to point to a dummy web server hosting a block page.  It is relatively easy to set up and reasonably easy to maintain.

Disadvantages

DNS Poisoning has the limitation that it can only block a whole URL, not a page on a URL as more sophisticated filtering methods can. It is also very easy to bypass, as all a user needs to do is change his settings to use a DNS server outside of his ISP connection, and this can be done very easily by many children today. 

Who Uses DNS Poisoning?

DNS Poisoning is currently in use by countries in Scandinavia for the blocking of Web sites containing child sexual abuse images (CSAI) which are illegal to access in most countries.  The list of blocked sites is supplied by police authorities in their respective countries.