The Problem:
Google does not index web pages, it indexes URLs, for this reason it does not automatically understands that http:// MyWebsite.com and http://www.MyWebsite.com is essentially the same page.
This can create two problems:
- Google thinks you have duplicate content; not great for your search engine ranking.
- External links may use different format of the URL to link to your site and Google will not count all of them towards one URL thus diluting the potential impact of the created backlinks; not great for you search engine ranking either
The solution:
First you have to decide what your preferred domain (Aka canonical domain) is. In other words you need to decide if you want the world to use www.MyWebsite.com or MyWebsite.com and let the world know. And than:
1. In your WordPress admin area under Settings>>General enter the chose format into the WordPress address and site address fields

2. In the Google Webmaster tools ( If you do not have an account yet, check out my post: How to setup Google Webmaster Tools )
- You will need to add the site twice. Once with the www prefix and once without it.
- After you verify ownership on both sites, go to site Configuration>>settings and select the prefer domain

That’s it. You are safe !
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