As of October 14th, 2014, Google analytics now warns users of having Redundant Hostnames causing hits to their analytics.
Many users are now seeing the error: ‘You have 1 unresolved issue: Redundant Hostnames.’
This means that there is more than one domain that can be used to access a particular page. For example, the domain example.com has redundant hostnames because it is accessible from www.example.com and example.com . This issue can also occur if your site is accessible by its ip address. For optimal user experience and seo practices, webmasters need to 301 redirect traffic to one consolidated domain.
In addition to providing 301 redirects, there are some best practices you can put into place to ensure your content is not duplicated across hosts.
The first is to add the following line to your robots.txt file:
Replace example.com with your preferred host, be it www.yourdomain.com or just yourdomain.com
Google Webmaster Tools also allows you to set a prefered hostname under “site settings”. This will ensure that your host is consistent across all traffic from google. You must have the www and non-www versions of your site verified on WMT in order to set this feature.