Google, and the other search engines, score websites based on a number of factors. From this score they subtract penalties based on whether or not they believe your website is trying to unduly influence the search engine results. One of the most common penalties is for duplicate content. Duplicate content is where the same content (or substantially the same content) exists in more than one place. If you are doing this intentionally you will get caught and you will get penalized. Even if you are not doing it intentionally it doesn’t mean you won’t get penalized! There are two common ways that legitimate webmasters can run into duplicate content problems.
The first place many webmasters run in to problems is with the use of www in the website URL. In many cases the www in the website address is “assumed” to be there. This means if you enter http://seoexpertise.ca or http://www.seoexpertise.ca they should both point to the same file and in most cases they do. The problem is that to search engine these are URLs pointing at two different websites! If you are using Google Webmaster Tools then you can tell Google which domain you prefer as your main URL.
There is a similar problem as that described above and that is what to do when you have registered two domains but you want them to point to the same content. For instance I have a client that has this domain, www.netsweeper.com and this one, www.netsweeper.ca. You will notice one ends in .ca and the other in .com. For this client the content for both of these domains is the same. In the past this client’s webserver was not configured to treat both of these domains as if they were only one domain. As a result of this configuration the search engines were treating each domain as a separate website. Knowing that a duplicate content penalty existed I made sure the server administrator changed the configuration to avoid the penalty.
It is very important to make sure your webserver is configured properly.